It'll be good to have someone go shopping again so we can update what you find. One bite at a time and soon you're wheeling in a deuce and wondering what to buy next.
Master Cylinder
I did a quick search for ""M135 Master Cylinder"" and found a few sources so unless someone has an extra one here, ,,,'search' for someone close to you. I think they were around $114.00.
Seat covers,
I headed to my local, small guy upholsterer and he knew what to do. Same deal with searching,,,, I found a few Beachwood Canvas types so you just need someone close and convenient. Matching material was a little tough so we hope you find some good canvas.....and take pictures.
Seals and bearings
There is a little challenge with the outer seal, "updated, out of date", part # 9427, and they may be more difficult to find than the inners.
When you're talking to the NOS suppliers, ask what they might have on the shelf for the outer seals.
.....part # D, Seal Assy 7411340
.....Federal Stock # 5330-741-1340
.....mfg part # YT-2280659
The inner hub seal on post 588......
http://www.steelsoldiers.com/showthread.php?52255-G749-preservation/page59
......does not have a manufacturer but after a search for "2275398" seal found a bunch of suppliers...here's one
http://www.partsriver.com/2275398-72280291.html