Several references are made to the dtvhacking forum, which can be found Here. The dtvhacking forum is a great reference for anyone interested in converting these 'joygames' into a working Commodore C64 (well, almost...)
My old, out-of-date DTV website is Here. There are several DTV/AVR hacking projects listed there.
Hummer modified games:
Sparkfun.com has the accelerometer and the RF modules.
Either the 315 or 434 mHz RF modules will work (lower freq might need longer antenna.) Also, the current modules look a little different than what I purchased. They did indicate at the time they were planning on switching to an improved model (not sure if it's 'Laipac,' but it looks compatible.) Sparkfun also sells AVRs, cool sensors and lots of neat gadgets for the hacker.
Although the accelerometer used was triple-axis model, a 2D version is adequate for joystick emulation (even a 3d accel isn't enough to truly simulate movement--you need a few gyros, too.)
Digikey.com is an excellent source of Atmel AVRs. In fact, I think they sell every Atmel makes...
The Digikey part # for the 3.3v LDO regulator is 497-4258-1-ND
The mini analog joystick was removed from a PS2 controller. Even brand-new ones can be found for $6-$10 if you look around...
Transmitter box is an iPod case. Cost: 3 cases/$2. These are tougher to find cheap, but there are so many iPods out there.... The shells are bound to get cheap.