Any old IC producing RC5 or whatever code will do at your sending end. I
would think that the easiest thing to do would be to break down an old
remote control handset, and cull all the necessary parts to make your custom
sender. I'm not sure if there are any dedicated decoder ICs still available
these days though. As far as I know, just about every piece of equipment
that uses remote control, carries out the decoding as a background task of
the system control processor. It would, however, be a trivial job to program
a PIC to do the job, and I am sure that ready written code modules for just
about any commonly used data format, would be readily available for free
download on the 'net.
Arfa
Radio Shack (yeah, this was long ago) used to sell matched modules for
this, but I don't have any and am not sure what was inside the modules. It
must have been something pretty cheap and off the shelf though.