There are a couple of guys on eBay which regularly have 50-100 auctions at any given time. Some disappear after a while and never list again, others pop back up after a few months of inactivity. There are a few "shop" level sellers who do have, at any given time, well over 200 items listed. Usually BIN for 30 days at a time though. If you're looking for a list of some of the bigger sellers on ebay of vintage parts, check out the "sellers list" on VeloBase.com. I keep a list of sellers there who have agreed to let me use their photos from their completed auctions, most of them regularly have a dozen or better listings.