I have posted some dungeon pillars in the second post. It includes some original (i.e. hand-drawn) statue bits in addition to edited RTP material. I hope it's useful!
I usually post things as add-on images, so that you can put them in a tileset yourself - so they do have to be formatted. Once I get more material, I'll turn them into actual sheets you can just download and use in RPG Maker. In the meantime, you can check out this guide, as it goes over adjusting and adding tiles to a tile sheet.
Been scratching away at my game and making progress, but just had a revelation. I'm working in full screen and adjusting all my pictures accordingly, but will they resize if someone's screen is smaller?? I hope this doesn't turn out to be a problem later.