I think there's still a backlog being caught up on from the multiple Battlebots and Robot Wars teams that emptied the stocks. An alternative option that is similarly priced is the IFI Victor/Vex 885. Handles 120A continuous and 200A bursts if I remember rightly.

Edit: here's the link; http://www.robotmarketplace.com/products/IFI-V885.html

Planning on using these myself, purely because I have a 60A version already as a spare. Slightly cheaper than the Vypers but you do have to get the PWM cable as well. The fan blades are prone to breaking from shocks so you'd be as well removing them, saving a bit of space. Biggest thing to watch is that the FETs don't touch, otherwise it's bye bye controller/repair time.