You can purchase most of what you need to do it at the Scamp
on line store and probable most RV stores. The Scamp
online parts store sells the main parts of what they use - so you have a good idea as to what your looking for:
Scamp - Sealand 711 toilet
Scamp Shower Faucet
Scamp 16 & 19 Shower floor
They use a thin fibreglass panel or laminate on the walls. On mine it looks like it may have been an old counter laminate sheeting.
If you do not have a hot water tank you will need one to use with the shower. Scamp uses an Atwood 6 gallon
You will also need to install all the plumping - most if not all the parts are on their online shop as well as common to most RV shops. Scamp also uses a pump under the shower drain to pump the water from the shower area to the grey tank - or at least they did on older trailers such as mine - do not know if they still do and sell one or not.
Edit: The black tank is part of the Sealand Toilet they sell. But you would need to add a grey water tank