A good place to check is the English Tack Trader Facebook group. The only downside is that it’s not as “official” as Ebay so you need to do your due diligence– ask lots of questions, ask for lots of pictures, and make sure the person is reputable and representing the saddle accurately. Only do your transactions through Paypal, and make sure the shipper gives you the tracking number from the post office. That said though, everyone so far I’ve interacted with on that group has been honest and very helpful.
Actually, there is one more downside…you’ll see tack ads from the group sprinkled throughout your Facebook feed which is really tempting!!!