Two types I have used are the ASO and a SpeedBrace
I'm not sure how available these are OTC.
BTW, if he has a severe enough injury where he has a ligament that has not healed properly, he might need a surgical repair down the road, especially if it keeps getting reinjured. Ankle braces aren't magic. Also, I know AirCasts enjoy lots of popularity, but I do not find them useful to limit inversion or eversion.
Vivian Abrams DPM