ENVF is difficult to find here in Europe.
-- frankbartoli

Looks pretty easy to me: https://www.planktonelectronics.com/store/envf/

Also, why add another set of inputs when there are these expensive Vermona ones already there? I can think of lots more sensible things to do with another 2 hp, and all that's needed here is JUST the envelope follower. No point in the rest of an Ears being in there.