I have given this some thought, and something like this would be a service to the DIYers around here.. I have many parts laying around from decades of designing stuff and even some inventory from my old kit business, so I would likely be more of a contributor than recipient. That said the only way IMO for this to work is to run it like a small business.
When people contribute parts, they ship them to the central warehouse prepaid and advise central book keeping what the parts originally cost. The contributor earns a credit when his parts are bought by somebody else... The buyer pays 100% of shipping cost to him, + a handling charge. + The price of the parts should be something nominal like 10% of original cost, more or less.
The problem is that this is bunch of work for somebody, including accounting, packing and shipping, etc. The handling add on has to be fair, but not billed at my hourly rate.. 8)
I have a bunch of parts, but I value my time too much to give them away... maybe if I could give them to somebody else to give away, it would be less painful.
Just my $.02
JR