If you search for disc detainer locks on ebay you won't find much because hardly anybody knows what they're called lol. Usually they will appear among the cheapest results if you search for "high security padlock".
And chris, as for tensioning, it doesn't matter where the driver disc is. The sidebar will bind nomatter where you apply tension, of course if the front disc isn't a driver then under tension it'll be "overset" so to speak.... but there is a trick to getting that one set, which lies in the fact that you can set the discs in any order because they're so poorly made.
I do have one of the rear tension tools, but I only use it for padlocks with the big plastic bodies where the normal tool won't get in deep enough to grab the front disc. Thankfully it isn't necessary otherwise, because it's very cumbersome to use.
