HP-A, B or C? I'm pretty sure the HP series has been discontinued. Unless you find one unused you will have to find used ones. Parts are still available for them from a variety of airbrush stores. eBay is also a good place to look for HPs. Bargains can be found.
You may want to consider posting a hello in the Introductions section saying where you are from, what you paint, how long you've been painting, etc.