Year One had a couple of 'glass vendors. One was Glasstek but I can't recall the other offhand. One of the two also made fiberglass N96 and Six Pack air cleaner bases and lids. Glasstek shows none of that stuff on their site.
I'll be talking with a former co-worker who was there for 19 years in R&D on Tuesday night. I'll try to remember to ask if he can remember who did that part. They might still have the tooling even though Year One doesn't sell it anymore... but it was 20+ years ago, so no promises.