I currently have a single Nav radio w/GS connected to a nav antenna via
a triplex coupler with 2 Nav and one GS output, and I have one Nav
output from the coupler that is not being used now.

I want to add another Nav radio w/GS to my plane. I can use the extra
Nav output from my existing coupler for the new Nav radio, but I need
an additional GS output for the new GS receiver. I know there are
quaplex couplers with 2 Nav outputs & 2 GS outputs, but they are
expensive. Questions:

Can I use a GS duplex coupler connects to my single GS output of the
existing triplex coupler to get 2 GS outputs?

Is there any plan available for a home made GS coupler?