I got a few of them, pretty complete. I think I got one from OPGI, and the rest straight from AMK. The one from OPGI was an AMK kit, I just googled what was on the little tag in the kit and went straight to the source. It seems most of the ones available from a lot of the vendors are from them (at different prices). Poke thru all the catalogs, they'll have just about anything you want.
Also, if you decide to order direct from them, do it online. The shipping will be a flat fee. If you do it over the phone, you'll get charged the actual shipping cost, which in my case was a bit more. Lesson learned, next box I needed I did online.
https://www.amkproducts.com/master-kits/chevrolet/
https://www.amkproducts.com/catalogs/order/pdf-kits-catalog/