That'll be easy but custom. Talk to upholstery shops, You could actually diy this.

My father did this, cost $90 per chair, 3 months. The time was due to sourcing the covering.

Any reason why you would not ask a local high school?

It's probably not possible to get a seat ready to screw into your chair. It is pretty easy to replace the fabric on the seat. And the foam, if need be. As you can see, the fabric is probably stapled to the seat. You need to be careful on the corners and put the first staples in the middle of the sides, working outward.

The worst part of the project will be getting up all the existing staples.

I can get the screws back into the board once I take them out which is why I was hoping to get another cushion with board so I can drill new holes.

can’t get the screws**

One method of dealing with the holes 'stripping out' is to use wooden toothpicks and Tightbond wood glue to partially fill the holes. This reduces the hole size and the screws will bite again. Try it on your seats. it works fine and is a commonly recommended fix. I'd choose this over the alternative option of using the next larger width wood screw from a hardware store.