Color 5x7 has not been readily available for years. When got my 5x7 9 years ago there were maybe two color emulsions available in slide film and maybe that number in negative. Think about how many 4x5 emulsions have come and gone since then. It was never a standard format for color shooters. I believe the publishing industry dictated the 8x10 and 4x5 standard. you don't go into 5x7 to easily shoot color. Even then you had to work at it because the cost was insane.
Back when we were a two income family and there was a bit of extra cash I worked with one of the die cut manufacturers to create a die to cut 2 5x7 sheets from 8x10. It would cut and notch five sheets of 8x10 with interleaf paper. Total cost was going to be 50 dollars US. We went to one income and all extra money went away so the project disappeared. Since I am a teacher I just called the company that made the dies we had in our workroom and they were the ones I worked with.
I did all that about 7 years ago. Buying and cutting 8x10 would have cut the cost of the film in half and the die would have paid for itself after the first box of film.
Where there is a will there is a way. In this day and age when emulsions are disappearing right and left you either accept it and do what you must to shoot the film you want to shoot or you pick up a digital camera and shoot that because it is easy. I am plenty happy with the selection of 5x7 black and white on the market.
5x7 is not dead it is what has been for a very very long time, a niche market within a niche market. If that Deardorff is cheap and you don't want it point the seller my way. Seriously.