Massdrop or a similar platform might make a good option for organizing a group buy. You need to find enough other people with the same desire for a given part or item, but everything else seems pretty well handled; I know plenty of folks who've participated in Massdrop buys for keyboards, Cherry-stem keycaps, and the like, and haven't heard any complaints about the service. (Haven't used it myself, though - I'm just going to get two sets of PBT caps off eBay when this year's keyboard-cleaning cycle comes around - so can't speak to it personally.)