I've got about 9 360Q's on my work table right now that are going through a complete refurbishing and I'm also going to need some washers. I plan on buying them from either Norcostco or BMI Supply. Good luck! Remember to use all aluminum rivets!
www.norcostco.com
www.bmisupply.com
I have trouble navigating or finding anything on the BMI website. But if you can, ask for their catalog. It's very helpful and they list lots of parts for 360Q.