Try Litko's BaseMaker™ tool. Choose to have your base made from any of 20 different materials. You can even get special features like rounded corners on your bases.
I used Litko 30 mm hex bases for placing Battletech Mechs on. Mechs that don't come with any bases, these bases are absolutely PERFECT for. Mechs that have flat bases on them still work extremely well with these bases, just a little putty around the edges and after the basing goes on you'll never be able to tell. Litko bases are a perfect choice for those looking for an alternative for Mech bases