Sorry for the late response but no, I have googled many places and it appears there are no instructions or anyone who has successfully sewn a synthetic sleeping bag.
I have found instructions for Down Sleeping Bags, Down Quilts, Synthetic Quilts, some minimalist synthetic bag by Bill Fornshell on this site, but someone actually doing a full all out synthetic sleeping bag with shingle construction or even just offset quilt, I don't think has ever been accomplished. Digging into my Nostalgia file I could have sworn there were home made kits by Frostline and Altra for Synthetic sleeping bags, but both companies are either no longer in business or they have changed there business plan.
With all the cottage industries that have kind of been bred by this website and other do it yourself sites you would think that there would be some crazy cross eyed seamster or seamstress raring to make an American made Synthetic Sleeping Bag and a legendary name for themselves. They could even have perfect vision and create these instead of having to worry about down flying all over their garage, basement, office, or living room and not having to worry about those foreigners stealing all our jobs. (it may only create one job if it is a cottage industry) Seems like it would be easier to make than a down bag which has baffles and of course the challenge of putting the down into the shell without making a giant mess.
Also, I think that Wiggy's guy needs the competition. He is probably bored being the only one making an American made synthetic sleeping bag, unless Kifaru makes their's here in the States. I think Caribou Mountaineering out of Chico California use to make Primaloft Bags but their quality control went to hell and they moved the company to Alice Springs Texas and I don't think they are even in business any longer..............
I was hoping the Quenemoen twins of Jagged Edge Mountaineering would have made a cool Synthetic sleeping bag with that logo of theirs which was coolest, but the company stopped making gear. They broke my heart, but I still have my Primaloft Jacket and Waterproof Breathable rain jacket.
Hopefully some creative type will step forward and take on the challenge.