They won't have shipped the piece for this. The manual covers two different versions of the scope. The first is the scope, on the CG5, and the second is the OTA on it's own. With this, there is an 'balance bracket', which allows the assembly to be fitted to a tripod.
This piece, is just like the part at the top of the GEM, that attaches to the dovetail bar, but has a 1/4*20 thread to allow it to be attached to a normal tripod.
Since they certainly used to supply this with the OTA, a 'wanted' ad, may well find somebody who has bought the tube to attach to another GEM, and who doesn't need this part who would sell it for a small amount. Alternatively a call the Celestron, should be able to source it.

Best Wishes