Jason, heed the good advice from Kalin and get new springs and washers from Deere when replacing the thumb release (pin) knobs. I too would have to think the part from Deere would be mild steel just like the original.
Jim's Lawn & Garden and HAPCO have offered stainless steel versions of the thumb release. Click on websites above to check them out.
I'll offer a low budget repair if the knobs have just "Vice Grip" marks and rust pits in them. First, screw them onto a 2-3" bolt for handling and remove as much rust as possible. Use a hammer to lightly peen the marks to a smoother contour. Then use a flat file to blend the high spots to the O.D.
Dip them in primer and let dry. Sand and repeat until marks are filled. Dip or spray green.
If there was a lot of metal gouged away, deep grooves, etc., you will probably be better off with new ones. Expect some of the paint to wear away with use.
tommyhawk