I got a Rhode Gear childs seat from a friend but they needed the Blackburn rack they had for it to go on for there next seat, where would I find out what type of Blackburn frame I need to fit an Appollo Phaze mountain bike with disk brakes. Thanks for any help or pointers.
Go to the Blackburn website and look through the disc compatible racks, or find out what rack your friend has and get that one. Or look in the seat's manual.
The Amazon spiel on the Blackburn EX-1 Disc Rack (or the manufacturer spiel) lists the copilot seats as compatible.
There is this previous question which shows that the seat's manual specifies particular racks, so you should consult it before purchasing a rack.