Anything similar or greater in ratings.
It is very important that it is rated 15v or higher, and typically the same value or higher. I've used 18kuF @ 50v before in a pinch as they were new surplus @ the local shop for $2 each and even they work fine. But if you're ordering, stay equal or greater than the original specs (value, voltage and physical size).
They are typically called "computer grade capacitor" and sometimes "large can" -- any big electronics distributor sells them. I typically ordered them from Mouser but I'm sure they're less expensive from elsewhere now.. Try newark, digikey, jameco or tedss. Don't buy them surplus unless the date code is recent.