Also, I've seen Rokugan Stuffed into the Forgotten Realms, easy. Conceivably, a character could have travelled to the "main part" of Faerun by ship, or overland routes.
But, if that's not your thing, anotehr name for Samurai could be "sword saint" or like someone said "cavalier". For Sohei, either Templar or maybe "guardian" or similar.