That's because they're not reproduced. You will have to find good used floor pans or modify Mustang pans or custom make some.
Are the entire floors gone in your car - as stated, you can get pieces or entire Mustang floors from CJ Pony Parts in Harrisburg Pa. but they will not match perfectly - they will need work to fit but will work also to the site from Northeast Pennsylvania
Mustang floor pans from CJ's is what I used in mine. Just a little massaging and fine tuning and they look great!!! from Ohio!
I figured we would have had an answer to my "Are the entire floors gone in your car" by now and then they we could attacked the why part