CS also used a company in Toronto named Acco Asman (check spelling, might be AKKO Assman) to make plastic molded tanks but that was way back, ran into company at Toronto Boat Show Jan '11 in Pickering or Ajax, ON that will make plastic tanks to order, so you should be able to get them the way you want them.
Was at Holland Marine in May, didn't like that there were no prices on anything, but did get the A&H port gaskets I needed.
CS was really astute at sourcing product from non-marine suppliers (interior cabinets, railings, castings, etc.) and keeping production costs down. You can try Brewer Brothers Marine Supply in Hamilton, they seem to have virtually everything or can get it.