Spaenur is available thru Adams supply over on Wall street, but best bring a stool for the sticker shock. They are not cheap. I imagine that is the place you were talking about back in post #3 in this thread.
Go on ebay and punch in 1/4 round slot screw into the search window. Lots to choose from.
One thing to consider as well is if you are restoring older equipment, plated bolts may not be correct for what you are trying to repair. Pretty much anything produced these days is.
Here is another favorite of mine for slotted screws along with other hardware.
http://www.fmwfasteners.com/products...Machine-Screws
I have bought a fair bit of hardware from them and even had them phone me if I specified "plain finish" and all they had on hand is plated. Plain would have taken 3 days to get, and they did not want to hold up my order.
I normally had them ship to my border parcel service, so can't remember if they ship directly to Canada.