I had the same luck...looked everywhere.
I discovered that if I can get a 1/16" male thread to male thread coupler I can attache it. BUT I can't even get that.
So I just rigged up some tubing and odds and ends to get it working, not pretty but it does work
These folks sell the JBJ replacement bubble-counter and check valve units for a reasonable price. I can say reasonable cause I just spent twenty dollars at Home Depot trying to make a co2 regulator I own work with this new planted tank I am setting up.