If you have a Mars, you need to pick up the
KO PROPO Mini-Z RF Module RF-901SM for use w/ your MR-03 (NOT to be confused w/ the non-Mini-Z version which will not work). Let us know if you need one and we'll get it in for you.
If you don't already have a Mars, check out the
KO PROPO Mini-Z EX-1 UR Transmitter 2.4GHz ASF SS set which we are having a sale on right now...