Happy to help out Ian but I hope this doesn't make things too easy for you
I found these guys LINK who seem to offer overland and dungeon mapping, at first blush looks quite good.
Then these guys LINK who might be useful, here's a screenshot LINK.
I didn't look closely but I think they want money (who doesn't?) but at least you have us to share the cost
There are loads out there and these just took a few minutes to find, but then again they did have easy links to follow