Let me start by saying that none of the above mention sell patterns. That is the "trade secret" of their business and generally considered proprietery. The Wisconsin upholstery shop does NOT offer kits and would likely be insulted as he is more of a tailor-type in the upholstery business.
I guess a couple more things to answer specifically what you queried is how accurate, or authentic are you looking for? Generally speaking, if you have a seat that has a cover on it, then you have your pattern. Just use a razor blade to slit the seams. If not, a roll of paint masking paper and a few yards of clear plastic will let you 'template out' the bare springs. Next is the part where you will need to sew everything. I don't know if you have, --or have access to a commercial sewing machine but that is gonna be crucial too as a home type unit is not going to make it through the first row of pleats. On the other hand, if you just need something clean to sit on and authenticity is of no real importance, then a trip to your local Wal*Mart or fabric store can probably yield some "hides from little Nauga's", some batting, a staple gun & staples, and some hog rings where you can cover everything and be riding in a day. Good luck in whichever direction you choose and welcome to the 'barn.
.
