Since we get about 10 or 20 posts/per day in the jet sale forums it's not monumental to search for just those items in there or using the search feature. What I may do is have a popup list in those forums where you could narrow down the search to the sub-categories or something like a filter of sorts.

I'm working on that for the events calendar and once that is done I will try to port it maybe to the for sale forums too.