I'm supposed to go jam with a buddy of mine who plays harmonica and I think he only has harps in Bb and C, so I need some songs to work in his keys. Any help would be awesome guys. Going through what I play, I realized I play in Am and D mainly.
Well, there's always the capo....

Kind of depends what style of harp the guy plays. If he's a blues player, then he's likely using some variation of the "cross-harp" technique.
The most common is to use a harp a fourth above the key of the song/guitar, so that the easily-bent draw holes fall out on the right notes.
So....With the guy's "C" harp, you'd be playing in "G". Easy. B-flat... Try playing in "D" with the capo on the first fret. (to make E-flat)