You are not going to find a new, code compliant toilet with more than a 14" RI...they do not exist as new. The best you are likely to come up with is a 14" RI toilet that you cheat as much as you can when attaching the bolts while keeping the outlet pointing down into the toilet flange without obstructions and then live with the extra space behind the toilet.
The advantage of a TOTO that uses their proprietary UniFit adapter is that a 10, 12, or 14" Unifit, on a 10, 12, or 14" RI flange position are exactly the same toilet, and will stick out into the room the same exact amount. Most others sold as 10 or 14" use the same bowl, but then make different depth tanks to fit the space behind , meaning, the toilet could stick out much further from the wall than one that can use the UniFit adapter and no, it doesn't work on just any toilet...the toilet must be designed for it.