O.k. I took a shot at a 3-digit eagle shield. I just made a blank shield in the Shield Generator, stretched it horizontally 125%, and pasted the state name and the route number 142, which I think would have been a better designation for OR 42S.
I'm not sure I have the aspect ratio right, though, just took a guess. Anybody better than me at this can feel free to improve on it, like one with the exact same eagle as the regular shield (not a distorted-by-stretching bird) and a consistently-wide border.
Anyway, it looked alright to me. I think it could be made to work.