I got my door latches at rvsurplus.com. But as pointed out above, you can find them at many places online. The one reason I picked RV Surplus (at the time) was the option to key the two latches alike for a small fee. I went and checked and don't know it that is still an option.
My doors (and walls) are about 1 3/8" thick. Since that latch is for a 1 1/4' to 1 1/2" thick door, it turned out perfect.
The walls are made as follows: the outer skin is 1/2" ply, the frame is 1x material and the inner wall is 1/4" ply. I used a 1x6 (see 1st pic in previous post) where the door latch is (and hinge side also) to make sure the latch (and hinges) was surrounded by solid wood.

