"RV shower pan" copy and paste those keywords for internet searches. You won't have any trouble finding what you need if you use the right keywords. They come in a variety of shapes and sizes.
You will need to do an addition search for wall panels, they do not come with the RV shower pans. That is because there are way too many variations of sizes in RV bathrooms and there is not a good one size fits all solution.
You are not going to have a lot of luck trying to find a kit with walls and the pan from stores such asvHome Depot. A house with a tiny shower stall you have no room to move around in is not something any stick and brick home owner wants to have. The smallest standard home store shower is 32 x 32.
Ebay is a good source for an "RV shower pan"
For your convenience here is a link to that search criteria
https://www.ebay.com/bhp/rv-shower-pan
When you look at the images you will notice that there is a flange on some of the sides, That is so you can have the waterproof wall covering come down over that flange to keep the water from going behind the paneling. Knowing how to install the wall paneling is important. Be sure you use the right kind of adhesive, some construction adhesives are not compatible with all types of shower wall and pan materials so do read the installation instructions very carefully.
Note that some of them have a pre-drilled hole for the drain and others do not have the drain hole drilled. The predrilled option has an advantage in that the metal pieces for the drain end up being flush with the inside of the pan and the pan may be sloped down to that point to help eliminate standing water. But sometimes because of various framing members and "stuff" below the area of the shower you may want to locate the drain yourself.
Note that some of them are made with Styrene types of plastics and others are made with ABS. The ABS is the stronger plastic.
Note that some of them have a riser spot for a toilet that can drain into a black water holding tank. You likely won't be needing one of those unless you are putting a black tank that can hold toilet waste underneath your RV.
Hope that give you enough information to help you find the perfect shower pan. If you can't figure it out then hire a handyman to install it for you. Do the parts of the labor you are comfortable with and leave the rest to someone else.