You have both Left and right boards? Check the other and see. That said, it is I believe #6/32 x 5/8". Sorry, to late to run out and check mine.
Should be able to get what you need at any hardware store, Rona, Lowes, Home Depot, Home hardware, Canadian Tire, or fastener store etc. Best to use stainless. Wont be to hard to find.
Edit: checked online and it is #6/32 x 5/8".