marxists.org is a great resource. My study group has had some growing pains, but it’s helpful to start reading some material during the sessions, like Lenin’s Left Wing Communism: An Infantile Disorder

Hmmm, I would suggest sometimes also going “off the beaten path” a bit in finding material; you never know what you might find.

@redjoker@lemmygrad.ml is right to suggest marxists.org but it’s good to have other sites that you know of that can be used as well.

Also if you’re a party member of an organization with a publishing arm, you could get discounts on bulk orders