If he's after a decent gaming mouse a cordless laser mouse is really not suitable imo, it's really not the same thing as the MX518 at all, however it may 'look'.
Being left handed does restrict your choice quite a lot, but it still leaves you with some excellent options, such as the; Razer Salmosa, Razer Krait, Razer Diamondback, Razer Coperhead, Razer Lachesis.
As far as none Razer products go, there is the ; NZXT Avatar ...and well, now I'm stumped, I can't think of any others that are of an ambidextrous design. There are no gaming mice designed for left handed users specifically that I can think of.
Razer have been more or less the only company making mice that left handed gamers can comfortably use for years now really. There are plenty of none gaming mice to choose from, from other companies, but none of them have the specs or the precision of a purpose designed gaming mouse.
In my opinion, the best alround pick from that lot will be the Razer Diamondback or Lachesis.