This is what I got from this company.
http://discountwheelandskate.com/pnwh.html
They were $18.95 each, pneumatic, nylon hub, and weigh about 1.5 lb each. They do have a 10mm bearing in them so you will need to sleve them or use metric mounting. They are going in a 33% Grumman Ag-cat which is going to be weighing in around 50 lb.
mac49