Adding a relief zipper

I still have my first drysuit that is very lightly used, largely cuz it does not have a relief zipper. Was going to sell it, but now want to add a relief zipper so my son can join me on the ocean. Has anyone know of a reliable place to have the zipper installed. It is a Stohlquist who has apparently gotten out of the drysuit business. Any leads are appreciated.

OS Systems or USiA might be a good place to start. If they won't do it they probably know who can.

Also, brace for sticker shock. The part is not cheap, probably in short supply (like everything else), and fairly labor intensive to install.

Look at this thread from Zach.Dennis
Using similar materials and techniques, you could do this yourself.
https://www.northwestkayakanglers.com/index.php?topic=20817.0

Just saw this in another fishing site, no idea about quality but they add zippers to waders and suits for $80 + shipping
https://www.facebook.com/waderzipper/