Hello, any help or advice is ver much appreciated!

I am wondering if and where I could get a custom sized tub made. I live on the first floor of a two flat in Chicago (long skinny house) and we would like to redo our main bathroom. We do not have a tub in our house, just 1 shower. It's 40" x 35". Could I get a tub made to fit this size? Obviously an adult would not use this as a tub. They would stand in it and use it as a shower.... (with the existing shower head... and the drain would still be in the center, as it is now). It would just be nice to have a small sized tub for my 2 year old son and any future children to come. Have you ever seen anything like this before?

Thanks! Doug