The battle grid in the DMG is double sided, and the second size sounds like it might be what you are looking for. I'd recomend removing it from the book and examining both sides before looking elsewhere.
Failing that, you could look in you FLGS for back issues of Dragon, which has occasionally included battlegrids of a variety of designs, suitable for different locales (city, underhround, an arena and others.)
If you want a better solution and you don't mind parting with substantially more cash, I've seen and covetted a lot of commercial products. There is a tile based offering out there that's laminated and intended to be used with dry erase markers, and also some 3d sculpted offerings.
By the way, if you happen to have small children, take advantage of a synergy bonus: my daughter's lego-like big blocks happen to be at the same scale as the standard battle maps. We usually use the standard blank side of the battle map in the DMG, and lay down blocks for the various walls. Works better than it sounds...