Afer I bought my M1009 last september, I asked the same question. I made notes and found that you can get seats in good shape at the wrecking yard. Look in the S-10 blazers and trucks, The seats from the Olds Bravada were said to be the same as well. I found a set of blue ones that are in excellent shape. Then I ran over to the Auto Paint Supply and had the guy mix up some SEM upholster dye for Vinyl. I am waiting to cleand and dye the seats until the weather warms; but I understand that if you clean it well and prep it right, you should get a good result.
Jatonka on this site has a webpage where he sells canvas seat covers for the M1009 to keep em fresh.