The issue with getting good buttons off of a radio is that they are secured so well that getting them off often will involve breaking them-
I have heard that putting the buttons in boiling water will help get them off, though have never tried it. Of course, to do that, you would have to dis-assemble a donor radio to just submerge the buttons, not all that hard to do.
To find a donor radio, ebay always has a bunch, find one that is "not working", you can get that cheap, or as the previous poster said, a swap meet is always a place to find a radio on the cheap.
If there is any better way to remove buttons, I would like to know myself-I havent run across a way in three years of looking for that answer.