You might be able to buy the exact replacement from here:
http://www.nldriver.com/product/product225.htmlIt appears to be a constant current driver. You say 650mA; the spec I found above says 300mA.
Once you decide which it is, you can just look for another constant current LED driver with the appropriate input and output voltage. I didn't find any with a quick search, but I only spent 3 minutes on it. You are presumably more motivated than I am.
In order of priority, you want the right current rating, then the right input voltage rating, then the right output voltage. You can compromise slightly on the last one, perhaps.
RoHS is a certification ("Reduction of Hazardous Substances", meaning lead free solder, among other things)