You mean in England? Tough to say; at least a few probably visited thanks to trade and human trafficking. Almost none would be the traditional peasant stock that Little John's generally portrayed as. There is a recent modern tradition of giving the Merry Men an Arabic, and sometimes black, member; Nasir, Azeem, Djaq, and others have all been interesting attempts to expand the makeup of the Merry Men.
Foxx being Little John does worry me; the actor has serious chops and charisma, but there's really only two ways to play a black Little John. Either he's going to be a radically different take on the character, in which case he honestly might end up either the worst piece of the film or the most interesting spin-off character, or the England being used is following the King Arthur tradition of fudging historical perspective to the breaking point.
Of course, even the usual film versions trying to be historically accurate often fall laughably short; if you want John and Richard as the Monarchs during the time, then they should be speaking in Norman French, with John being a capable tactician if a poor strategist, not some insanely incompetent untried nobleman or personification of the Evil Brit stereotype, and Richard giving less of a rat's @$$ than just about anyone about England outside of the economical benefits of having a crown.