Hi Paddy,
you can also use other brands like Hitec (e.g. 322), but you´ll have to use an adapter or rearrange the cables in the connector, because the old Airtronics connectors had a different pinout than current servos are standardized to. It´s all described in this nice article:
http://jacobwatson.com/images/dads%20images/connectors.pdf
Herbert