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I got my last ones I needed at Gravel Agency Inc. Also there is a guy that has a ton of them in all of the different shapes and thread sizes and lists on the EE from time to time. Unfortunately I forget his handle but he is in Nova Scotia
Cheers
Any decent gunshop should have an assortment, which they buy in a kit form. They should be able to order what you want if they don't have it in their kit.