The only time I've ever had a problem with the fuel caps was at Atlantic SJC. Nowhere else in the US has this been an issue.
The caps are pretty nice, actually, because you can stick your hand on it and feel if it's properly closed by whether the button in the center is down. You should make that part of your preflight, by the way.
Does your airplane have the anti-siphon flap inside the filler neck?
Also, are you saying that Twin Commander can't provide the caps any more?
If so, that's good to know, because they do wear out. We used to have problems with the center fuel caps on 690s, because they got used all the time while the wings were used less often.