If you have a household budget, just make room in the budget for the P7. You won't get what you paid for the P229, so unless you just don't care either way hold onto the P229.
What reason does your wife have for this "wife imposed restriction"? Do you have a similar "husband imposed restriction" on her love of jewelry or shoes (or whatever hobby she has)?
I have a "hobby account" much like what oktagon suggests, as does my dad. It is not some secret "slush fund", rather it is money that I decide what to spend it on without discussion. I earned the money, the bills are paid and if I want to buy a gun I use the money from this account. If I don't have enough in the account to get what I want, I wait until I do. No secrets, no deceit, just no committee meeting. That's the way a household budget is supposed to work. Maintaining a separate account removes the chance for a miscalculation, or shortsighted impulse. This also keeps arguments from occurring.
Also, there is no reason that both parties cannot have their own "hobby account" in the household budget.