Help!!! I need new toilet with a 18" rough in

I am remodeling a basement in my 100 year old custom home and the toilet has a rough in at 18â€. Dose anybody have any ideas on were I can buy a toilet that will work? Or is there any kind of adapters that can move the rough in back to 12". Any advice will be much appreciated thanks in advance.
Stuart

No such animal exists. Keep in mind that some older toilets had a couple of sets of bolts holding it to the floor, and the real drain might be closer to the wall (if you're lucky). The alternative is to either build a shelf behind the toilet so it isn't sticking out into the room, or move the flange back where it needs to be. Have you taken the toilet off and measured? The value is from the center of the drain to the finished wall behind. Usually, you can just measure from the bolts, but not on all old toilets - you need to remove it to measure.