Here is a link to a really good virtual Harmonica which works with Native Instrument's Kontakt. Somewhere I read that it may require Kontakt 6, but I can't find the source of this information at this point.
It's only $22 on sale, and after buying it, I can testify that it is ultra simple to install and sounds excellent.
It works very well with windcontrollers, keyboard, as well as with the Tech breath controller as you can see and hear with the demo samples.
Let us know if you get it and how it works for you.