Wow, I am looking for the same thing. Rallysman has convinced me to build my own though. Whatever happens first I am going with but I dont think I can finds one in enough time. Good luck on your search.
Do it yourself! Mine took some work, but its working GREAT on my 90g. I think all of it cost me about $150 or so. I am pretty sure it would work well with a 125.. maybe just have a little more standing water in the bottom and add something for polishing.
Just make your own. It will only cost a fraction of what a wet-dry sells for, and can be made out of just about anything that holds enough water. Besides, most of the ones I've seen for sale don't have enough sump space IMO.