I have been using old Lyman .348 gas checks. With a thousand to a box, they should last a while. Original 71, regular, not the deluxe. RCBS bullet. Or old Hornady J-words. 4064 powder. Might want to check old Handloader magazines for info. I think Barsness had an article on it. Most Lyman manuals should too. Enjoy it.
Here is a link to the article I remembered. It wasn't Barsness after all.
https://www.handloadermagazine.com/the-348-winchester