It's a small thing but those were not factory. If you take one off the maker will probably be molded in small letters on the back.
You can view dealer brochures at
Toyota 4runner Touchup Paint Codes, Image Galleries, Brochure and TV Commercial Archives but he charges to view. Those are called turbine wheels and they were a style in the 80's. I did not say popular but I guess they were. There were 5 lug for Jeeps and 6 lug for Chevy/Toyota. I've seen them on muscle cars too. I bought an '88 4Runner new and they were not offered and I never liked them anyway. My dealer would put aftermarket wheels on so I got Outlaw II's. Those are the "bullet hole" wheels you see on 80's trucks.
You mentioned getting steel wheels. Aluminum wheels are lighter so get slightly better gas mileage if that's an issue for you. You should be able to get some 15" Tacoma or 16" 3rd gen 4Runner aluminums for about $80-$100 a set from Craigslist.
Sorry for the boring history. I love your new 4Runner. Have fun.