Try a marine trimmer loft, take board and bag into shop, and let em know what your after. You can still get away with using same board bag and zips, I've converted a couple in my time, easy if you know what your doing.
Thanks for all help and suggestions. I got a Creatures Of Leisure 7'6" / 2.3m Surfboard bag that fits perfectly. Purchased online for $129 with free delivery