What I found in the parts on Troy-Bilt's website was this:
MC-6228-202004A SPOOL CARRIER ASSEMBLY (NOT SHOWN)
MC-6194-202001 WIRE-CUTTING

To purchase, please call toll free 1-800-269-6215 between the hours of 8am-6pm Monday-Friday or 9am-5pm Saturday EST.

The only thing is that part number is different, so I'm not sure it's correct, but looks like it in the diagram. And 2nd, it's still just the spool and separate line, so I think we'd still have to wind it, which most people complain they can't figure out how to do.

Let me know if you find anything better.