Who’s your mentor? Used to know a few people who paddled C1 and OC1.
Guy from uni still makes them (c1) http://www.shaggydesigns.com
There was a well known coach around the North East who used to open boat (Ken Hughes? I think).
I never really understood it. I prefered tow blades as it gave more support and power, also a damn sight easier to roll when the inevitable happened.
Just noticed that was the Etive. Nice run that, only done it once with a couple of locals after a training course. They were in Creek boats, I was in my playboat. I ran it all blind without inspection (just going off their instruction) as it was going dark. Scared me a bit!
CAn’t help you on the foam although canoe shops often have it at ridiculous prices.
ukriversguidebook as always may have the answer.