Where to buy tension extender?

Anyone know the best place for tension type extender systems?

Most of those devices have been talked about in the Review Forum. You can look through there for links. The least expensive and one that does not have a noose-type system is the PeniMaster. There are several threads on that device alone and several of them have links to sites that sell it. Use the search feature, button top right of every page, to find the threads. Or you could make your own.