I found the upgraded hubs from another site sponsor. But they are almost $82 per side, so replacing both sides ends up being just shy of half the price of the disk brake upgrade... Links below for your viewing pleasure.
Ausco Disk Brake upgrade (Doesn't fit stock size rims IIRC):
https://www.jasonsgolfcarts.com/EZ_G..._p/brk-202.htm
EZGO hub upgrade:
http://www.cartpartsplus.com/brake-h...ts?search=hubs