For digital: https://www.amazon.com/MakerFocus-NRF24L01-Transceiver-Antistatic-Compatible/dp/B01IK78PQA?crid=2E0BS0WE0H3WB&keywords=arduino+rf+transmitter+and+receiver&qid=1537634702&sprefix=arduino+rf&sr=8-3&ref=mp_s_a_1_3
More standard "analog": https://www.amazon.com/RCmall-Precision-Controller-Transmitter-Helicopter/dp/B01BZQ15L0?crid=1PUH18BA4PNEB&keywords=rc+controller+and+receiver+kit&qid=1537634855&sprefix=rc+contr&sr=8-1-fkmrnull&ref=mp_s_a_1_fkmrnull_1