You’ll need to have the paper duplexed, as you won’t find anything this thick. You can just print both sides on the 300, and then find someone to duplex it (our offset friends here in Chicago are capable so you can probably find someone close to you).
Crane Lettra. Absolutely THE finest high-gsm paper available. It is LUSH to say the least. But the customer better be willing to pay!! LOL 🙂 It is available in 220 lb 600gsm duplexed cover. IMO the finest letterpress paper available. And at $75 for 50 sheets it better be! 🙂 Jessica @ Rolling Frog Press