I am assuming you are referring to the concrete paver slabs. These are poured in place concrete slabs which gives us the greatest flexibility in the sizing. You can purchase some pavers off the shelf but the sizes are limited. For example Mutual Materials provides concrete pavers is 24"x24" , 18' x 18" and 12' x 24"

https://www.mutualmaterials.com/products/24x-24-concrete-pavers/

You may want to check w/ you local masonry supply company.

I hope this helps

Dave Giulietti

GSW Architects