You might be interested to read another thread which involved, IIRC, one of the fill ports or some other part on our tanks. I think it was Skillet's tank. Long story short, same type of deal, where a call to Manchester revealed the part number, but you have to order through a distributor, etc. etc.
At the time I thought I might be having some trouble with the shut off level dohickey inside my tank, so I tried to get the part through PPL but was never successful. On the other hand the problem turned out to be, from what I could tell, clueless fill employees, and so I didn't continue searching. Skillet was able to get the part he needed through his RV place that was working on the tank, as I remember.
Might not be same part, but the discussion might be useful anyway. I'll see if I can dig it up and come back and add a link.
Okay, here it is:viewtopic.php?f=4&t=328&hilit=skillet+propane+tank
BTW, speaking of the low-hanging ports, I have found that some places have a hard time getting the long filler schnozzle thingie on and off the tank, because the place they have to attach it is low and angles down, causing the schnozzle to want to hit the ground as they try to attach/detach it. I found that if I run the three right-side tires up on a few Lynx blocks that helps. Even better, when I went to a "real" propane place they have a soft, hose-like extension they can use instead of the rigid filler nozzle itself - works perfectly. Now that I don't have a propane fridge anymore, I can usually fill up there for the year and not have to deal with the other places