I have a suggestion for the transmitters I had a similar problem when looking for a pre-made remote's for a Traffic light system I made for loading bays in work, I came across "AM Keeloq" Transmitter's and receivers.
The transmitters are 1-4 buttons, they are Encrypted (keloq) so they cant be copied easily but more importantly they have a unique serial number which the receiver can read via a serial output the transmitter is designed for 4 buttons it has momentary or latch operation, basically a garage door opener, however as I've said the transmitter's have a serial number so it should not be hard to associate a specific transmitter with a specific task in your program.
oh the receiver has built in memory and can store 50 unique remote's (although you wont need to memorise them as you will be using the serial output)