I'm not a MYOG person (you should see me try to thread a needle!), but I do know that the gear firms who were formerly using spinnaker (Gossamer Gear, Mountain Laurel Designs were the main ones) have discontinued the use of spinnaker because they have not been able to find a source of this fabric that is suitable for shelters and packs. There is also a durability issue with spinnaker; it is quite sensitive to abrasion. I have a spinnaker tent and its stuff sack, also spinnaker, is worn out after 3 years. I'm replacing it with a silnylon stuff sack. I note that those "cottage" gear makers using cuben fiber (also sensitive to abrasion) for their packs are switching to a hybrid fabric of cuben and nylon or polyester, for the same reason.

I do know that Thru-Hiker is an excellent source of fabric, kits, supplies and DIY articles. There are also great resources on the home page of this site.