The only dual throttle that I've seen is the one from SunCom, the
SFS Throttle. You can still find them on the Internet, like through e-bay.
It's almost to much of a pain in the bellybutton to get them to work to make it worthwhile. You have to have Win9x, it won't work in Win2K/XP because the programming software is incompatible with Win2k/XP. If you plan on using pedals, you have to make sure the pedals are USB, otherwise you won't get the dual throttle, stick and pedals to work at once. If you have all USB gear and intend to use the dual throttle with that, you have to have an extra analog joystick handy so you can use the programming software.
The benefits in AH aren't all that great, it doesn't put you at an advantage over someone using a single throttle but it does make hammerheads a lot easier to pull off. I switched back to my Pro Throttle after about 3 months with the dual throttle.
Ack-Ack