Some vendors at gunshows have the little parts like springs, detents, etc. you can buy separately. Just get a list of what's in an LPK and buy the parts individually. It comes out to be a tiny bit more than what a regular LPK without the price gouging is going for. Then you can pick your trigger and pistol grip without having to have an extra pistol grip and trigger group that you didn't really want.
A majority of those little parts run like .95 - 1.50 each.