Kohler bathroom faucet connector hose

I need a faucet connector hose that is 5/16" compression at one end and 1/2" FIP at the other. All the hoses I can find are 3/8" or a few 1/4" by 1/2" FIP. The 5/16" compression screws onto a male 5/16" that is part of the faucet system. I got absolutely nowhere with Kohler---won't take phone calls, never responded to emails. Any idea where I can get this hose or an adapter that converts a 5/16" male to a 3/8" male? Many thanks from Big Island of Hawaii. And I have gone to Ace, Home Depot, and Lowe's and they had nothing at all.