Without knowing which arm has been disabled, it's tough to offer specific advice, so I'll just shotgun some ideas here.
First, assuming you can still use a right-handed mouse, might I suggest the Logitech G600. It's got tons of buttons, which assuming your right arm is the functional one, can help fill in a lot of gaps with some creative mouse button configuration. And before anyone cries foul, yes, it IS superior to the Naga which it obviously borrows its design from; I own and have thoroughly used both. The G600's software is also superior.
For left-handed use, either the Razer Nostromo or Logitech G13 gamepads. I have both, and while Logitech's offering has a lot more extra buttons, I find the Nos to be generally more useful with its scroll wheel and more ergonomic feel, while the G13's advantages are more buttons and a true anolog stick (though in a very awkward position, unlike the Nos' more comfortable d-pad). The Nos also has an adjustable palm rest unlike the G13.
Those are off the top of my head, and granted are only mainstream devices and not anything specifically made for the disabled, but I hope I've helped, or at least given a direction to pursue further. Best of luck with the gaming! :)