I got it from here:
http://www.ebay.co.uk/itm/120802352134?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
Yeah, I know, you get what you pay for, but I only needed it as a fairly simple controller and the seller had very good feedback.
The system profiler says:
USB-Serial Controller:
Product ID: 0x2303
Vendor ID: 0x067b (Prolific Technology, Inc.)
Version: 3.00
Speed: Up to 12 Mb/sec
Manufacturer: Prolific Technology Inc.
Location ID: 0x1d100000 / 2
Current Available (mA): 500
Current Required (mA): 100
Is that what you meant?
Thanks.