Well.... what should I do if lowes AND home depot somehow fail me and don't carry steel pipe? it is in plumbing section at lowes or home depot right?
if not is it even worth attempting to buy it online?
Do not put dollars before safety.
In other words: Yes, it absolutely is worth buying it online. Hell, I buy most of my pipe online if for no other reason than I'm a lazy SOB and don't have to leave the house that way. Plus, for weird stuff like that often desired for spudding, you can get a much larger variety of pipe. Want a 4" pipe nipple 12" long? No problem!
Aside: Seriously, where do you live that Lowe's and Home Depot don't have racks of steel pipe and fittings?
... I honestly can't travel to the ends of the earth or crap out a piece of hardened steel, so no need to laugh at my possible injuries as a result of my unsuccessful trip to the store
Look back at my first post in this thread. I told you the story of a hobby I was involved in. I realized that there were two ways to do it. Expensively. Dangerously. When I realized I could not afford the expensive route, I simply dropped the hobby. It's not like you can't pick the hobby up again later or your life will somehow be incomplete if you can't build your airsoft mortar.
If I told you I had a car but it didn't have brakes and I wanted to drive but just couldn't afford to have the brakes fixed you'd call me stupid, right? No matter how badly I want to drive or how much fun driving is, it's DUMB to drive a car without brakes, right? Thus, the only rational course of action is to not drive the damned car until I can get the brakes fixed...even if it takes months to do so.
My point... If you can't "travel to the ends of the Earth." If you can't buy it online. If you simply can't buy metal pipe for your chamber given your resources... STOP RIGHT THERE! DO NOT PROCEED FURTHER! Simply accept that you'll have to play airsoft without a mortar and get on with your life secure in the knowledge that you'll still have ten fingers and two eyes when all is said and done.