My earbud covers ripped, so I looked at Target for another pair. They didn't actually sell covers that fit my earbuds, so I had to go without. The earbuds are surprisingly comfortable without the covers, so I think I won't bother to find and replace them.
I guess if you are comfortable, more power to you. Are you still happy without the covers? I think they are also supposed to protect from moisture but I'm not entirely sure.