Anderson doesn't make SB-50 contacts beyond 6 AWG. I believe most of the teams that elect to use larger wire simply remove enough strands at the end to make the wire fit in the 6 AWG contact.
(The SB-120 connector supports 2 and 4 AWG wire.
It was banned for last year, but I think FIRST should switch to that size just because its rating matches the rating of the Main Breaker. The SB-50 was acceptable when you could only use ~10 motors. We can use up to 30 now.)