Not sure what it may be called today, a few years ago it was called the roof termination trim.
Searching online I didn't find it by that name. Allrite has all kinds of trim but not that one.(that i found)
The last I bought, I picked up at Bontrager's in Michigan.
I'd probably try the local dealers next.
A simple way to clean that is to make a soaking pan out of aluminum foil. Pour enough mineral spirits in, 1/2 inch or so, to cover and wipe it off every 30 minutes or so until clean. Lets you do other things while the mineral spirits does the work.