I finally beat GRPD an hour ago or so (my strategy: hold two Mirror Darkly shields, which I bought, and blast Dred with Pearlescent wands, which I crafted). I was going with a pure-mage build the whole way. By the time I got to DL15, I was wearing a ridiculously powerful Hat of the Space Wizard, a ridiculously powerful Sash of the Blue Wizards... and a mage's robe, a kilt, and no shoes. For the last five levels, I was surrounded with all kinds of ten-star armor, but none of it was at all appropriate for a mage. Where's the magical love?
there is a wizard armor called the cloak of Sagan. very powerful for wizards. there is also an armored archmage robe, there is a recipe to craft it with smithing.
One of the interesting dynamics in the game is that warriors are highly gear dependant, and thus get huge armors and weapons that make them hoss, but also have to deal with corrupting monsters on a much more regular basis that ranged fighters. On the other hand, crossbow users and wizards have far fewer equipment options that will directly help their strategy, but it will last them much longer. On a side note, there is better gear than the mage's robe for the wizard armor slot. Armored Archmages Robe is typically the best you see, but if you get lucky you'll get the Cloak of Sagan. If you didn't see something in that neighborhood of power, it's probably the fault of the RNG. EDIT: Nicely done, Ruigi.
Magic Sandals are the only wizardly shoes, and I think they're craft-only items (like The Mana Torus and the Ring of Iron Thorns) - they can be made with 5 Alchemy or found in a Brax shop, but otherwise you'll never find them in the dungeon.