I am currently gathering parts for my Expanded Momus build and thought I would share a few suppliers with other builders in Canada that McMaster Carr will not sell to.
Before I found out that MMC would not sell to me I had purchased a 3/8-8 4start anti backlash nut and coupler from Dumpster. After several failed attempts to purchase from several suppliers (most were not in stock) I came across the Roton Products Inc. website. Their Torqspline lead screw matches the Dumpster nut very well. They have other lead screw and nut products as well. The lead screws are sold by the foot and pricing is in line with the least expensive of the other suppliers, shipping cost was about $40.00 for two screws and 1 nut ( For the heck of it I bought a two start screw and nut as well) Shipping took less than a week.
Nuts and bolts being as expensive in Canada as they are, I found it worthwhile to purchase the hardware mail order from the U.S. I bought more than I need from The Nutty Company and with shipping was less than I could buy wholesale locally from Canadian suppliers.
I did a comparison on the metal parts and found out that buying from Online Metals was cheaper by over $100 even after shipping, when compared against the local metals superstore.
I hope that the difficulty in sourcing parts hasn't deterred too many Canadian builders. These sources might be of some help, though as usual, shipping costs are important to watch.
Cheers,
Matt