Help: rear end question

[007ojitos]

Hello,
Ok, please read--heres my dilemma. Sorry in advance if its wordy.

I have a 2008 ezgo st express, 6ppl, stock kawasaki gas power cart. I am in the process of upgrading it.
I want a little more speed, but cant find anyone who supplies parts for this cart, since it seems much of these parts are either from a txt or a workhorse depending.
Mikes motor toys was a great help and once said that i need to put a high speed rear end on it. A whole new rear end. I havent been able to get a response back though since im sure hes busy.
My question is: what are my options?? Anyone know of a supplier for a gear swap for this cart? If i need a whole new rear end, a part number/place i can order it? Lastly, if im getting a new rear end, is it one i can take off a used cart, and if so, what years/model?
Im desperate for some help here, thank you in advance...