Well it looks like I made more fuss about this than was really warranted.
I bought this hose on eBay, which I believe is a standard commercial 2" hose as far as dimensions go.
http://www.ebay.com/itm/140883117028
In case the link goes bad the eBay seller is universal-hose.
It has a double layer. The outer layer looks like a thick spiral of blue plastic. The inner layer is black plastic. (Note that Shop Vac calls their
hose 2.5" but that is an OD not an ID. The Shop Vac hose has a 2" ID. The commercial guys go by ID not OD.) They sell the hose with and without cuffs. The auction w/o cuffs has a closeup of the hose construction.
http://www.ebay.com/itm/SHOP-VAC-INDUSTRIAL-VACUUM-HOSE-2-X-15-NO-CUFF-BLUE-/360508470300
Please also note that when these auctions refer to "Shop Vac" that are not refering to "Shop Vac" the brand, but just the generic term.
It turns out the the OD of the cuffs on this eBay hose will friction fit into the ID of the Shop Vacs threaded inlet. The fit is good and tight. And it works well with the other Shop Vac wands and attachments. So no special adapters are needed. The cuffs are of that harder-than-rubber-softer-than-plastic stuff. Probably some kind of vinyl?
Anyway, soooo much better quality than what Shop Vac tries to sell you. Case closed. Thanks for your help.