@Geektastic pricing from ChopMate to make a board to my supplied specs using Tasmanian Blackwood was very reasonable I thought, so thanks for the recommendation - definitely a possibility.

I've also located someone in Canterbury who makes custom boards out of a variety of woods, including North American Hard Maple. I haven't got pricing for my requested specs yet, but he has been very helpful and informative; and based on pricing of other boards he currently has I'm hopeful it will be within budget. And I really like the idea of him being (relatively) local so I can see some of his finished work in person before committing. So another good option I think.

I will almost definitely get one custom made, as pricing seems to be no more than buying a pre-made one - but has the advantage of getting exactly what you want.