Of course I could find a few things here and there but I don't want to order from 10 different stores and pay for shipping for each screw. This was a little easier when I was still living in Germany.

I'm in Canada, and I've built quite a few things that float (in the Toronto area and also in Victoria BC) and I've found that the best prices and selection are available from 'specialist' suppliers. Trying to buy everything from one source is cheaper for shipping, I admit.

For me it is often a question of: "I need a dozen SS machine screws- should I buy them in bubble packs @ 50 cents apiece, or get a box of 100 for $6." Same with abrasives, though you do need to store them (unlike hardware) in a dry environment.

And it makes a difference if you are in a metropolitan area- local pickup can be easiest, though I speak from my status as 'retired' so I can go shopping during working hours. ;-)

For fasteners (though you probably don't need enough to make the minimum quantities worthwhile) Fastenal is my favourite. Get the SKU's from the website and contact your local outlet. They can have everything bagged and ready for pickup.

For fasteners, sealants, cordage, and perhaps paint a marine chandler is the place to go. WestMarine locally or Jamestown Distributors (but they won't ship anything liquid to Canada, IIRC). Noahs is a good source, they have reasonable shipping charges but insist on packing cans of paint loose in oversized boxes with stryrofoam peanuts (Yes, I've gotten back to them about it, but they repeated the same thing on the next order, and then ignored my emails after that...) so prepare yourself for seriously dented cans.

I've had good service from Newfound to Canada.

The MAJOR problem with US suppliers is their frequent insistence on using UPS/FedEx with the consequent bogus and $$ 'brokerage fees' (I don't mind paying the PST/GST/HST) - I generally only deal with places that will use USPS. (NB- you can even get burned by this if 'special ordering' a US item via a Canadian supplier, as I learned recently.... :-( )

If you are planning to paint your boat, make friends with your local autobody supply for epoxy primers and more (though you need to have good protective equipment and access to a spray booth).... also a good place for masking tape and abrasives.

For abrasives and some other finishing supplies Jeff @ Wood Essence in SK is excellent.

I've seen TomsTopKayaker recommended here - please let me know if you deal with them.