I have 2x Leviton L6-30 receptacles in good used condition. $10 shipped for one receptacle, $18 shipped for both.
Description: Leviton 2620-B Female Twist Lock Receptacle, NEMA L6-30R, 2 Pole 3 Wire Grounding, Rated 30A 250V.
L6-30 plug also available, Pass & Seymour new old stock. Same price as the receptacles.
Updated in new thread.