I have only found one place that sells a gearbox (azimuth drive
gearbox) for the Meade ETX 90EC telescope (telescopehouse.co.uk). 
However, they're not responding as hoped, in a timely fashion.  So I
sent them an email instructing them how to run a better business, now
I'm afraid I won't get a competetive price.  Please find me one or two
other places that sell this part, preferably online.

Broadhurst, Clarkson & Fuller have the exclusive distribution rights
for Meade in the UK, so you're probably out of luck. You could try
dealing with Meade direct, but I don't think they'd play ball.

Ian G.

The 90AT probably has the same gearbox.