The ccTLD for Mauritius is .mu. The e British Indian Ocean territories stop existing once the UK releases its claims to the territories so there goes the country code of "io"
With the demise of X.400 e-mail and IANA's general aim of one TLD per country, use of .gb declined; the domain remains in existence, but it is not currently open to new domain registrations.
https://en.wikipedia.org/wiki/.gb
NB I was curious as to whether .gb would be strict and exclude NI - who get to use .ie if they want...