Because I have a lot of stuff, I often get approached to sell, buy or help find items for other urbs. Since I'm out in the community a lot, I have a good pulse on who has what for sale, where to find things that may not be advertised for sale, and who has good prices and trades well.
When at all possible, I will put two urbs in contact with each other to make an easy trade, but sometimes I act as a middle man. I also try to use my previous interactions with urbs as leverage for new trades, or trades with newer urbs that have done right by me.
But, when I started this collection, a great resource for me was the Pawn Shop. I think that many times, this under-ultilized function has some great gear, especially for newbies. I can't tell you the number of times someone is looking for some reasonably priced starter gear, that I've gotten at a great discount from the shop and donated it thier way.
I've found in most cases, you can get an item below Funk's cost, and it's a good place to check when folks are dumping their inventory.
As a bouns, if you're low on funds and people aren't buying your stuff, the grump who runs the shop will take it from you. Granted, you may not get as much cash as you'd like, but hey, that's business....
If you're ever looking for a place to find something you might not expect, check the pawn shop. Or if you're looking for something, let me know and if it's there during my visits, I'll pick it up for you!