Is there anyone out there know where I could obtain a mercury vapour 125 watt H42 ballast that works? I am desperatly looking for one! Any advice would be really appreciated. thanks very much.   

I would recomend using 100 watt MH ballast with the ignitor deactivated, as it closest in the current specs
For 125 watt MV lamp.

so a 100 watt metal halide ballast with ignitor deactivated will effectively operate a 125 watt bulb?

so a 100 watt metal halide ballast with ignitor deactivated will effectively operate a 125 watt bulb?

Yes, exactly.

are 100 watt metal halide ballasts hard to come by?
 

where would you recommend looking for one?

It. Depends on how much u are willing to spend on the ballast the ballast to run your 125 watt MV lamp. ,  and  geographical Location. If u live in Canada  i would
Not buy the ballast from USA side as shipping can
Cost more than ballast worth .  1000 bulbs is great
Place but I am lucky enough to drive down just pick
One up there in matter of hours not have to pay postage.  Two if your not in a big hurry
I tend look for my ballast at a Restore ( habitat for Humanty)  more than one way to obtain a 100 watt
Metal halide ballast here.  You have all kinds of possabilty here.  On Ebay a proper 125 watt ballast
Shows up now and then, some times at decent give away prices. Like 125 watt Advance CWA mercury ballast i found for 9.99 and plus shipping when i found mine.