I don't own a 5 string, or 5 string mutes, but every 5 string play I know uses a normal 4 string orchestral mute, between the D and A strings like they usually would. The idea is they add mass, dampen the vibrations, and change the sound, so I don't think there would be much of a difference between a 4 and 5 string for that purpose.
As for practice mutes, I'm assuming you mean the huge rubber ones that go over the entire bridge? Again, the same ideas should apply, although I am not sure if the string spacing would be a problem. If you can take your bass to a shop and try one to see if it fits, or talk to them before ordering one and see if they will accept a return, that's likely your best option.
Sorry for not having a definitive answer, but a fairly certain, "I don't think they exist" is all I've got.