I've had three, and shot two of them quite a bit. Never had problems with anything breaking.
Except for springs, I can't think of anything that might need to be replaced. Wolff probably doesn't have them, so Century Arms International and Numrich (E-Gunparts) are the places to look.
Trigger and recoil springs are candidates. You can probably use springs from SIGs or S&W Third Generation guns for the recoil spring.
Magazines are in short supply, but mags from the S&W 59 series can work (but will extend just a bit farther than a flush fit.)]\
I like the the DP51 (and similar DH40) a lot, but for the use you plan, you'd be better served by buying a used Glock -- parts won't be a problem, and they are relatively trouble-free, resale will be easier, and the price probably won't be much more.