Why don't you want to use one of the vacant circuits from one of the fuse boxes under the hood? It's easy to get the wire from under the hood to under the dash, at least on the passenger side.
Behind the battery, where the harness comes through the firewall, is a nipple on the grommet. Cut the tip off the nipple and run the wire through.
The circuits marked in yellow are constant power. If it's not marked it's switch power. Pick one. The two circles are 1/4" spades that are hot. They just need to be fused. You can see the fuse tap I used on a vacant switched circuit.
Some context would help..
-What are you using it for?
-Location?
-Do you need switched and/or constant 12v?
-etc..
Anyhow, there's a few spots tbh. Could just use the 12vdc "cigarette lighter" ports. Or there's one spot that was extremely useful for me. It wasn't used on my trim at all, but still wired up and fused from the factory. It's an empty white connector above the driver's side map light. You have to pop out the map light assembly (very easy to do, just some clipsβgoogle the Meso Customs video on YouTube of how to install their aftermarket map lights if you're still uncomfortable, they pop it off in that video). Connector is "Option Connector W20" ...Not sure if you have TIS, but..