Looking for a source for loaded 8 bore shells.

Thanks

https://www.rockymountaincartridge.com/

Try http://gadcustomcartridges.com/

I suspect it might be cheaper for you to load your own using new brass 8 gauge hulls

Tom Armbrust owner of Ballistic Research does custom 8ga reloading utilizing swagged Winchester clear 8 ga industrial hulls. 815-451-6649
RST has 8 ga shells in development utilizing the Winchester hull. It is my understanding they are currently pressure testing samples so it may be worth contacting them to see if they have a target date.