As @fuzztone said, they are pretty easy to replace yourself. I did a pair of speakers recently and they turned out great. However, if you are not confident that you could pull it off, I would think Millersound would do them. I looked at a photo and they look like typical foam surround.
If Millersound won't do it, maybe try SimplySpeakers.
If Millersound won't do it, maybe try SimplySpeakers.