There's a choice of approximately 50 aircraft frequencies for use in the US with no licencing required, and another appx 10 for HAM licenced R/C aviation use. There is no FCC regulation about what size plane uses what frequency.

It is a good idea to check with the local club(s) where you would be flying, and try to get afrequency ythat isn't used by several regular flyers. If 2 people show up with the same frequency, you may have to wait 10to 20 min to get the frequency pin. If 5 show up with the same frequency, you might get in one flight out of a 5 hour visit to the field. (waiting for the pin and the instructor to be available at the same time...)