you can buy 2" schedule 40 galvanized pipe at Home Depot, in any length up to 10 feet.
Bury 3 feet will give you 7 foot pole.
If you need longer pieces, you might need to go to a plumbing supply store, and a more "industrial" one at that.
They should have schedule 40 black steel pipe in lenghts to 21 feet.
Your
HH120 needs 2" to 3.5" OD pole. This type of pipe is sold sized by inner diameter - so 2" pipe is actually 2.5" on the outside.