Where's best place to find walk--in seated shower to fit 40" space?

Lowes, home depot and other plumbing supply co

yes Lowe's has that but you're better off going to w a Bragg Plumbing on Mike Padgett Highway Highway 56 between Lumpkin Road and Peach Orchard Road

There is an entire section dedicated to that. It is located in the rear of the store. I'm sure an associate could point you in the correct direction.