I doubt you'll find a DM 'on demand'. Its no so much a multiplayer lobby 'waiting for host' type situation :) Most would want to schedule a time, meet the players, discuss play style and characters, approve characters created, go over his house rules (if any), discuss a setting and so forth. But if you create a new post, with what type of gameplay you guys prefer (roleplay, story driven, open world, monty haul, dungeon crawl, munchkin, what have you) , the game itself, timezone and time, length of session your seeking, and so on Im sure you can find a new DM for your next session.