Any hobby store can order/have one already, ofna has a one way check valve, it's what most of us used. NOT between the tank and engine, from the exhaust TO the tank, with the air flow going into the tank. This way the pressure can't excape when you let off the gas, takes away the lean issue. Before I did this I had to run the tank from full to half and refill or retune. The stock tank looks like someone took 2 tanks and made 1. It's fat on top and once it meets the frame it's about half as wide.

Glad to hear everything worked out for you. Hope it's in your hands soon.