Sorry I've only just seen this because we had exactly the same problem trying to book for our trip last March.
All the flights we were interested in were code shares with American so we eventually booked on American which accepted U.K. credit cards. In the course of doing this someone on this site gave me a telephone number for Hawaiian but I don't think I actually used it . I'm interested to see the U.K. agent as my husband spent a whole Sunday trying to sort this -and eventually did but we didn't know about that U.K. agent!.

I have found and topped the old thread for you