It's not hard to find historic routes after they have been long decommissioned. Note Azuza is misspelled, it's Azusa (with one 'z' and replace the other 'z' with a 's'). I been through those towns on I-210 on the way to LA myself.
It's cake finding them because they still exist as city streets. The problem you got down in the valley is that most of the really good structures east of Pasadena until you get t San Bernardino are largely gone with redevelopment. There is some really nice stuff on Santa Monica Blvd, Sunset Blvd, Colorado Blvd and even when you get to San Bernardino... I don't know, I've been really disappointed by the stretch between the two cities in the past given how much I've actually take the full route between the two... Here's what I'd recommend seeing 66 related or within the area if you going to go hunting for stuff in California:
- Santa Monica Pier: Must see since it has a lot of 66 related stuff on it.
- Petersen Museum/La Brea Tar bits: Located down on Wilshire, the automotive museum has a lot of really nice cars and a lot of pieces of highway history in the Los Angeles area. The tar pits are right down the street...so why not? Definitely take the majority of Santa Monica and Sunset though since you get a lot of that Old L.A. flavor that's getting increasingly rare.
- Arroyo Seco Parkway: Take the portion north of Sunset and get off on Figueroa, that will give you a solid look at the classic tunnels.
- Colorado Street Bridge: This is probably the most classic Route 66 bridge there is in California. You can drive over it and take some really cool pictures from the bottom. The Rose Bowl is around the corner too...you can take a picture of it if that's your thing. I would take Colorado Blvd through downtown Pasadena since it has a lot of older buildings and get on I-210 to get to San Bernardino.
- Original McDonald's Site and Museum: This is on the original McDonald's site in San Bernardino...it's more of Route 66 museum more than anything else and has some really nice old road signage on top of trinkets from the route.
- Cajon Pass: A must see divided part of Old 66 west of I-15 on Cajon blvd. This is a really cool place where you can get a look at what older Californian expressways looked like for about 5 miles and see the trains coming down the pass up close.
- Summit Inn: This is up at the top of Cajon Pass and is an authentic Route 66 diner. The food is okay but the neon signage is what really stands out.
- California Route 66 Museum: Interesting museum on D Street in Victorville that has a ton of old signage and display pieces related to Route 66.
- Lenwood Stretch: The stretch of US 66 west of I-15 goes through several smaller towns. There are some really old gas stations on the side of the road that are worth looking at and taking some pictures.
- Barstow Harvey House: I added the address for the train station in Barstow since it's an older Harvey House and Museum. They have a bunch of train and Route 66 stuff worth checking out.
- Daggett: You won't be able to access Daggett directly from Barstow due to the Marine Corp base but it's worth a look given how many older 66 style buildings are there.
- Bagdad Cafe: Apparently this was is a bunch of older movies even though it is closer to Newberry Springs rather than the actual Bagdad townsite which was east of Ludlow
- Ludlow: If you can get past the facade along I-40 there is a really neat ghost town south of the Interstate. This is where you are going to get off to see most of the Mojave section of old 66 anyways.
- Amboy Crater and Amboy: The Amboy Crater is a volcanic cone south of Old 66 as you are coming up to Amboy Road. There is a newer paved road to the crater itself, worth a look. Amboy itself has Roy's Cafe and Motel which is a really neat old complex. They sell some trinkets inside but nothing too worth while.
- Chambless: Chambless has a lot of old roadside ruins to it, my favorite is Road Runner's Retreat.
- Cadiz Summit: This is a couple miles east of Chambless is a heavily vandalized husk of an old travel lodge. Some of the art work on the concrete walls is fantastic.
- Essex: This is a neat little ghost town with lots of older buildings and gas stations, just make sure you stay in your car since there are a couple weird desert people lurking about with attack dogs to this day.
- Goffs: A really neat abandoned railroad town on the original alignment of 66 before it was straightened. Lots of abandoned buildings to checkout and a small museum with wonky hours.
- El Garces Hotel: This is another Harvey House in Needles which is an incredibly beautiful building now that it's almost restored. You can get a really good overlook from the McDonald's just off I-40 but there is also a small Route 66 Museum across the street with the building itself. Be careful of Needles PD, they like to screw with people passing through town on speeding tickets.
- Colorado Arch Bridge: If you get off of I-40 at Park Mobai follow the road east to the Colorado River. There is a white arch bridge with a pipeline on it which was the original car bridge over the River for Route 66. There are some really neat signs meant to attract you to Oatman, Arizona from here.
Basically that's my take on the entire state...lots to see but most of it is pretty limited in suburbia and will take you a long time until you hit Cajon Pass. The desert is really where Old 66 really comes into its own but it's a pretty lonely journey and not one a lot of people want to take given how far off the grid it really is.