There's a guy on Craiglist in Conyers that always seems to have Toyota trucks he's parting out, might be a good place to start. I was a Pull A Part late last week and every 4Runner motor had been pulled already.
If those places don't pan out then you're looking at a crate motor, without a core it's probably gonna cost you an extra $500+. I used The Engine Guy in Braselton last year but that's another story.
All that said and as the owner of 2x 3.0 motors the 3.0 is a decent engine but not popular by any means. Assuming you're doing your own install you might consider doing the 3.4 swap since you're already waste deep into it. Do your research, there's a ton of info on the web and depending on the tranny you have the swap is almost plug an play with the 3.4 motor.
On the 3.4L, I replaced the engine in my 97 4Runner with a JDM 3.4 from NA Auto off Jimmy Carter. I think the engine was around $1200. Only thing is the intake on it is from a right hand drive, so I had to reuse my LHD intake. It was 50,000 miles or less and they did a compression test prior to purchase.