They're just screws. I would think the first place to look would be your local hardware store, or better, a home improvement store.
Failing that, there's the internet, and probably some other stores around, depends on where you live.
I don't see much point though. Assuming you bought a tri-wing, I'd want to use it as often as could for better value, haha. It makes sense if you didn't buy your own tri-wing though.
Recommended Shops
Replacement Wii screws
Linear Mode
