The usual suspects (Ann's, FF, TRR, Collector's Square) have been discussed above in this thread, and have their pros and cons. There are a number of Japanese resellers on eBay (some with physical locations) that have also been discussed. The problem is that there are so many factors that go into being comfortable with buying pre-loved, and it's often a very personal decision. First and foremost is of course authentication. Some may argue but I think many members of this forum will agree and have articulated, again, all over this thread, that bababebi is the gold standard for Hermes authentication.
After that, it's a question of how far off of a boutique purchase are you willing to go, at what price, and with what set of inconveniences? I don't mean to sound flip, because I've done this very thing myself when on a mission -- you could type in 'black leather Hermes Kelly 32' in an Ebay search and start whittling it down. Eliminate sellers by any criteria you feel would make the purchase a 'hard' no. If you research leathers first, and have a hardware preference, that may help you eliminate another swath of candidates. Then it's zoom in and have a look.
I've seen bags at other resale sites but wouldn't mention them because I've no personal experience with them. That's what this thread is for. If you're a bit chagrinned at not finding a handy list, or places you've not considered, think about what you're asking. Frankly, were I in the market for those specs, and found something I was considering, I wouldn't tell you either. I've had things that I've had my eye on appear in the 'Post Web Finds' thread and thought "oh no, I wish that hadn't been posted!" and sure enough some other lucky person pounced. Again, not intending to be flip, unpleasant, or to gate keep; I do wish you every luck in your search, but beyond some basic guidelines and guardrails, it's a bit of a solo occupation.