I don't know too much about this "minor" stuff. I don't have any minor harps, either. They must be useful for something, but they don't seem to be necessary.
This gets weird, now. If this is Greek to you, don't worry about it:
If you want to play minor blues with a major harp, look at the circle of fifths. Lets say the song is in Gm. Don't look for the Gm on the circle; just look for the G. Usually, the best bet is to play the minor blues in 3rd position, so for Gm blues, play the F harp. (I don't understand how that works. I just know it's so.)
Minor harps