I used to run two 175 watt MH lights off of one PC4 outlet. If it is a higher powered device, or multiples like that run it off of port 1 or 4 as they are rated higher (8 amp). Channels 2 and 3 are only rated at 3 amp.
I personally would run a small splitter as opposed to another surge protector. As for where to get one I'm not sure, I haven't looked in awhile (sorry) have like 3 sitting around.