As such most companies only make bulk quantities of certain products. For example, they don't make both the raw material *and* the gadgets sold by Radio Shack.

The raw material for your pressure vessel is a polyolefin, a derivative of the petrochemical industry (we all know this is a big industry on its own). Bulk quantities of polyolefins such as polyethylene resin are made by companies such as Nova Chemicals. Some of the PE resin is purchased and shipped in pellet form inside tanker trucks to an extrusion company, such as Honeywell Performance Fibers which then makes thousands of tonnes of bulk fiber material for various industries. Some of the bulk fiber material (there is always a minimum purchase quantity) is purchased and shipped to a prepreg composites company such as Advanced Composites which combines the fibers with a matrix material such as glass, concrete, etc. in a manner specified beforehand by a customer. Bulk quantities of their composite parts are then shipped to the OEM who assembles them into a complete product, composed of other non-fiber, non-composite, perhaps even metal, electical, adhesive, moving parts, or whatever. The OEM then sells them to a distributor who then sells them to a retailer. You then walk into Radio Shack and pony up $200 for the fully assembled CD Player, which may be composed of some small discrete parts made of fiber composites, perhaps for shock resistance, or fracture toughness.

Polyethylene composite pressure vessel manufacturers in Canada? I don't think there are any. Most pressure vessels are used in the boiler industry, and I don't think polyethylene would be an appropriate material for that application. But there is a link here and you could simply call them and ask if they can answer your question about where polyethylene fiber might be used, and who uses them. Again, I would expect to get the run-around, simply because there are so many companies in the manufacturing chain.