Of course it's out of stock at the moment but maybe you can locate one.
https://www.ebay.com/itm/3-5-To-3-75...-/312401911237
This is the coupler I used. One end fits the inlet on the supercharger and the 3.5in end was a common size that I could find a PVC Pipe endcap at a local hardware store to hose clamp in the inner diameter. Drill a hole at the endcap and pop in a rubber tire valve. Voila!.