Looking toward swapping my '72 250C auto transmission to a manual, believe the manual is a 4 speed and am wondering who has one for sale and/or other parts needed; any direction is welcome too.

but you do know that you may need a different crankshaft, right? No problem, though, if you have the engine out and disassembled, and can get a competent shop to perform the work. (Crankshafts for manual transmissions need to be drilled for the pilot bearing. It's possible that some crankshafts were drilled but put into cars with automatics for the U.S. market, but I've never seen one. I mostly work with much newer engines. MB may have drilled all crankshafts back then, though.)

Here's an amazingly comprehensive list of parts needed for a similar conversion. I started to get these priced at the dealer, but stopped partway through the list when it reached $10,000:

http://www.benzworld.org/forums/r-c107-sl-slc-class/1488256-installing-4-speed-into-v8-107-a.html

However, this may fit your needs perfectly:
http://www.peachparts.com/shopforum/showthread.php?t=303509