I just bought a lot of ten L6-30r 250V Twist Lock Flanged Female Outlets. They are perfect for heater element connectors. I am not looking to make any profit on these. I paid $6 a piece shipped. I will sell them for the same price plus actual USPS shipping. I have 7 to spare.
As promised, here is the link the seller sent me. The price is for 10 packs. Get together and group buy it! I am not affiliated with him so direct any further questions to him. Take care and post your project pics!