The always resourceful Alban sent over a link to Vintage Printable, a website collecting...well, a little of everything. Vintage ephemera, medical illustrations, classic alchemical texts, old magic posters...there are well over a hundred different categories of material. All of it in high resolution, free of copyright, and yours for the taking.
This is one of those great sites where you can spend hours just looking at what's available. Site navigation is a little wiggy, but that's a minor quibble compared to amazing quality and quantity of the collection.