rf001-a receiver
If this is a one of a kind system, you can make your own transmitter and receiver.
For the transmitter use a microprocessor crystal in an inverter oscillator. Follow this by an AND gate. One input is from your oscillator. The other input is low for no signalling, and one of two different audio frequency square waves for a transmitted data of one or zero. Put a wire on the AND gate output for an antenna.
For the receiver use a TRF type, antenna, amplifier, diode detector, and PLL to tell which audio tone is used.