In high end speaker they are not always electolytics. They could be but there are some different types. You can look them over at Simplyspeakers and a few other places.

Anything other that a lytic of some of those ratings will be quite expensive, so unless you got really good ears forget it. One technique is to put a smaller cap like a poly or something across it, but then you have to recalculate the value. Easy to do, just subtract what you add.