Sugar Twin is also available in the US but it's made from a different sweetener - in Canada it's sodium cyclamate. I'm not sure where in WA Hartline is, but if it's anywhere near the border, a quick trip into Canada and you'll find it's available at any grocery store in the sugar and baking aisle.

PS - it measures spoon for spoon the same as sugar, so granular Splenda would use the same amount as Sugar Twin.