I'm the same as Dobbsy and Nuglug... Bend the bases, clip the bases, then carefully trim/pry with a knife.
As for replacements... Well it depends on what you want really.
Magister Militum do 40 x 15mm bases, and more besides
Renedra have quite a lot of bases or shapes and colours
Kallistra also do a variety of bases and sizes
Dark Realm Miniatures do resin bases with holes cast into them suitable for Epic figs.
Fenris Games and
Litko laser-cut bases from ply, MDF or plastic. They also offer similarly-cut magnetic sheets that you can use to stick your models onto a steel surface for safe transportation (like a steel toolbox for example).
Finally, you can always make your own like me and others here:

The way to do this is to buy two thicknesses of plasticard (I used 1mm for the upper piece and 0.75mm for the lower piece), and then measure a whole pile of bases in one go (so a big 'grid' of bases on the sheet). Then you score and snap them out. Gather the 1mm plates togther, tape them tightly with masking tape and drill holes through them. Take the tape off, and offer each drilled plate to a plain plate and -holding them together- dab the edges with a capillary-action plastic solvent (like Ambroid Pro-Weld). Finally, once the plastic is fully set, tidy up the edges with some emery paper.
It takes a while, but to make mine it took about 2 hours for 120 bases, and them about the same again to file and polish them all to a good finish.
The main advantage of making your own is that you can drill the holes wherever you want, and even different numbers of holes too if you like. I drilled all of mine to accept either three or four models to a base, and the sizes were 40mm x 15mm. As you can see, the bases do not look sparse model-wise - it really depends on what models you are basing, how big the base is, and how crowded you want your bases to be.