From Where can I buy a gas valve VR4601M2009?

My boiler is MYSON MIDAS Sfi 1993 I have got a problem with the gas valve. First it was making vibrating noise for quite a some time, but the boiler was oprating fine, but few weeks back it stoped working, I show pilot glowing even when I Cut off the power supply. So I asumed the gas valve was stuck, I taped on the valve, it released and pilot went off. I switched the boiler again and it started to work. But now the flame is not steady, it goes up and down, Now I am getting hot and cold water, there is no steady tempreture.where can I buy this valve from? I have tried so many dealers, they have'nt got one. Please help!!!!!!!! I have already put a new PCB and Heat exchanger about a year ago, I can't afford to lose all that.Thank you very much. Please help!!!!!!