The controller cable should be an ordinary plug-in IR emitter, available from any custom installation company.
The antenna should be available through RCA. Go to
[Link: rca.com] for a start and then go looking for parts.
I think all American UHF remotes run at 418 mHz. You can make your own antenna, although it might not be really sensitive, from RG-6. Take a piece of RG-6 and put an F-connector on it. (Use whatever adaptors you need to connect from that to the RCA's antenna input.) Remove 7" of insulation, braid, foil, and foam from the other end of the cable. This is your antenna, and is about a quarter wavelength. Place that end of the wire a few feet from any equipment and see how it works. This might not do you, but it is sure a cheap trick! I used such an antenna to extend the reach of a Pronto's RF signal.
A different approach would be to make a circular antenna such as you used to see on UHF inputs on the backs of TVs. This antenna consists of bare wire cut to one wavelength, bent into a circle, then soldered to the 300 ohm side of a 300 om to 75 ohm transformer. You then connect, through appropriate adaptors, to the RCA's antenna input.
One wavelength at 418 mHz is 28 1/4", and you will end up with a loop about 9" in diameter. This antenna will NOT pick up the signal when you position the remote so that it looks end-on, that is the skinny way, at the antenna.
I also had success with an antenna of this design for both receiving and transmitting FM; it's just that at FM frequencies, the darn thing is a circle 37" in diameter!