There are a few items now that are already unobtainable "new" , such as the wheel shrouds and the indicator kits. Not even Adam Harper has them available.
I remember watching a tv programme about restoring an early VW Beetle - a guy paid £250 for a rusty & dented front wing. He had to have it because it was the only one available for that particular model.
Similar thing with some C5 parts, and I expect that as Adam runs out of stuff things are going to become more difficult to obtain and therefore more expensive/valuable.