Besides seeking out training at the usual suspects (very expensive as I understand it, usually with a prerequisite commercial rating in some other category,) one other way is to buy a hot-air (thermal) airship and train in it - provided you can find a commercial airship pilot to do the training. I think Cameron Balloon may be one of the few commercial options: http://cameronballoons.com/airships.html
I found this Brazilian company with a $20,000 price for a Cameron built thermal airship: http://www.skyzepp.com/Hot_airship.pdf
I have no idea how realistic that is - seems low.
Or consider designing and building your own airship; good luck finding plans - and definitely no kits (which I find odd, given that airships predate airplanes). One starting point is the Experimental Lighter than Air web site http://www.xlta.org/
