After vendors, the "biggest" LRs have around 200-300 players. EternityRO had a massive amount of players but it shut down for the third time recently.
AtlantisRO has around 1,600 on average, but it's a Spanish server.
Talon and heRO both have 700 and 400 respectively, but that's before vendors - they've both been online a few years, though, so you can expect that at least 1/3 of their populations are @autotrade Merchants. DeePee or heRO's admin (forgot her profile name on RMS) would be able to tell you more accurately.
If those two aren't to your fancy, you may need to reduce your population demand.