I think it is not needed to create a totally new map, because there are already many intresting maps around.
True. I've seen similar effects achieved just by walling off a portion (or single territory) of a map with really high neutrals, like 1000 or more. There are plenty of medium/big/huge maps that could be adapted for this purpose with Custom Scenarios.
Looks like you need to get to level 47 ASAP to unlock Custom Scenarios! ;-)