Looking for a 1918 or earlier coupe
That would be called a Coupelet, unless you go back to about 1910 or so.
Few and far between. About thirty years ago, an article in the 'Vintage Ford' said there were two (I think) complete cars known (one was re-chassised in about 1922), and one or two parts car type. These were all the removable pillar couplets. Since then, several complete cars have crawled out of the barns and woodwork. One is in Europe, being restored (haven't heard from him in awhile, I hope all is still okay). Another body only was sold a couple years ago in the USA and hopefully being restored.
There I think is still a body only (however in nice condition and well worth restoring!) in Montana. I don't have contact information, and the asking price was quite high, however, I have been told the collector that has it is known to become reasonable if someone shows real interest.
The earlier folding top couplets (1915/'16/ early'17) actually seem to be more common. The removable pillar '17 and '18 cars are very interesting, as well as rare.