One bike has one fork. Of you're at a store and they have more than one boxxer, totem etc on display, then they are displaying "forks".
Referring to a single suspension fork as "boxxers" or "a set of boxxers" brings up some interesting questions. is it being referred to like that because a fork has more than one leg? Could you say "a set of leftys" when describing cannondale's single-leg design? Or does the single leg mean there's only one fork?
Am I reading way too far into this? Probably. But I AM sure that it's FORK not "forks".