Base layer bottoms with through the crotch zip?

Anyone know of a source for a base layer bottom with a through the crotch zipper?

I searched it on Google, and pulled up a lot of things I can't unsee, but nothing useful for taking a dump in the alpine.  

I have an old OR fleece salopette with a full crotch zip, but doesn't look like they make them anymore. I could be mixing it up but I think NW Alpine used to make something similar. 

You probably found this in your searching but apparently hunters are into full side zip base layers: https://www.kuiu.com/ultra-merino-145-zip-off-bottom/10004.html#

Might have the functionality you want if you zip both sides partially down and tuck the back flap in.

Also I'm guessing it wouldnt be too pricy to have a skilled person sew a zipper into your favorite bottom layer.

IME, they only make such with a salopette or similar.  I have one from FeatherFriends with a half moon zipper. HH makes something similar:

https://www.hellyhansen.com/en_us/hp-racing-midlayer-salopette-34049

I really like my Airblaster Ninja suit.  Its more than just bottoms but I have comfortably executed an alpine dump in them.

 https://myairblaster.com/collections/mens-ninja-suit