Custom battlemaps are actually derived from the larger map. If you have a look at the files, you'll see that each one has coordinates which tell's the game which part of the larger map it should generate - so you could find them all in the campaign if you wanted.

EB certainly has a lot more of the locations highlighted, but again you'll have to rely on campaign generated fields.

Plans are afoot, however, to give you some even more exciting custom battlefield options in an optional expansion after the Open Beta release.