Dave,
The old magazines aren't easy to come by, just have to be persistent in keeping an eye out. I have an interest in the subject due a Great Uncle who built trailers and motorhomes in the 20's and 30's, even have the original patent paperwork! I am on the constant look out for anything related now. I think we are a rarity in that area of interest.
We got an old Sunbeam T-9 toaster (better $$$ than Ebay) and some other old kitchen decor items and a crate and something else for display in the garage. Ebay is both a blessing and a curse. The antique shops around here aren't really that good anymore either. We chanced upon a couple shops that had stuff in Allen MI, but there was still plenty of serious junk that had to be looked over. We've found that if you travel around, you find that different regions will have totally different items from one another. The other strange pattern we noticed is you'll see something you haven't before, than go to another store or mall and see a couple more of the same. Go back in a month or two and find none.
As far as finding road ephemera, few and far between here too. You may chance upon some 50's era, but that is the extent. Back to Ebay we go....
Oh, did you see the two Lincoln Highway signs that sold on Ebay? One of them went for $900 the other was over $700, ouch! My pockets aren't that deep.
Jason