Keystoker K-6 coal boiler, stove pipe question

[crmoores]

Boiler is located in basement so I have a "T" and a 5' vertical run up the foundation and a 90 degree out the wall. Last winter was 1st season using it, has a direct vent and 4" galvanized pipe running from the direct vent up the foundation wall and out through the wall. The installer used 24 gage pipe (I think), didn't install it correctly and also didn't seal the joints so I replaced it all but couldn't find the 24 gage so I used 26 gage. This was a mistake I now know and figure I should replace this pipe with heavier pipe. My problem is the boiler is close to the wall due to space restraints and I don't want the pipe rubbing on the wall like it was when originally installed. Then it had 2 elbows between the direct vent unit and the straight vertical pipe. I used a "T" with a clean-out to limit the number of joints. But I can't find this smallish "T" in the heavier pipe. The heavier ones are "bulged out" and will not fit between the direct vent and the wall. So I'm considering moving the stove away from the wall which involves cutting the water pipes even though it will be in the way.
I want to ensure I have safe piping installed first and foremost.

I guess my question is does anyone have any ideas or references to sites that sell galvanized or stainless pipe? Is this "T" not appropriate for use here? Is 24 gage the normal pipe to use? I assume I should replace the 26 gage before firing the stove? Not many resources locally except for the double-wall pellet pipe. Is the double wall pipe appropriate to use for coal? This doesn't need the joints caulked?
Thanks!