There doesn't seem to be a hard and fast rule about autocephaly. The Church of Greece and the Church of Cyprus are Autocephalous, yet they both receive their Chrism from the Patriarchate of Constantinople.
A lot of Chrism is consecrated at once in a large cauldron, and very little is used at each Chrisimation. After a Baptism in the Greek practice, the Chrism is administered from a bottle which has a metal stylus on the inside of the lid which is used to apply the Chrism (a bit like the way some perfume samples are distributed like the ones below), so very little is used at a time.
