Set and save a "Search" on ebay for the dish(es) that you would like, and make sure you "tick" the box that pops up to ask if you want to receive emails about new listings of those because quite a few do pop up from time to time.
They often start at ridiculously low BIN or "Make an Offer" prices compared with the "buying new" prices, or they then just don't get many (if any) bids at all and sell for a pound or two because people just want to get rid of them and only 1 person did actually make any bid at all! To look for the latter set the search to "Ending soon"
That's more or less how I got my Gibby OP125L which I saw listed about 2 yrs ago when I was "just idly looking around" at what was on offer. It was very local (West Drayton) and there had been only 1 offer of around £70 some days/weeks earlier, so I made a "silly offer" of £85 - and that's what I got it for, complete with STAB motor (later proved faulty!), an Inverto Black Ultra, ground mount and cables. Took a bit of work (and my estate car) to get it back here, but has since definitely proved worth the money, effort and time.