I'm sure there are loads of similar posts on the forum about this but thought I would give a shout to George at Breville Customer Service.

A quick email about shimming and they have sent me a shim kit in the mail without any issues at all (in fact I asked where I could order one and they just shipped me one).

Thanks guys and really appreciate it - it will live on in my kitchen as my brew grinder for V60, aero, press etc.