I started this last night and finished today. This was my best flute project to date. I’m very satisfied with this one.
A PVC connector as an embouchure plate?!?!?! How come I never thought of that?!?!?! 
Nah, it’s actually a piece of 3/4" pvc split downt he middle and glued on. I thought about using a connector but I didn’t want to have to grind the ridge out of the middle.
You can buy the connectors without the ridge in them.
I’ve built flutes using the coupler before. A nice embouchure hole is easily made with a 3/8" dia. endmill drilled slightly off-center and then move it over 0.1" in distance to slightly elongate it. The ridge can be removed using a boring bar on lathe.
I use the couplers on whistles as well to cover the windway. I’ve not heard of couplers without the ridge, that would be nice.
They have them at Home Depot and Lowes.
They had them in neither when I was looking.
Maybe it’s a local market thing?
Ask around at plumbing suppliers for “slip” couplings! More common in larger sizes. Generally used for repair work where it is not possible to separate the pipes being repaired enough to use a regular coupling.