G'Day Chris,
I have got a EQ6 pro and the only place I could get adapter plate for my pier was from England .Off the top head I think it cost about $180 aus all up but then it was 2years ago .I tried a couple of engineering firms to have them make it , but they wanted about $400/$500 . You can try this site they may be able to help you out
https://www.altairastro.com