lol... ROHS is a european union LEGAL REQUIREMENT. That is NOT a feature. The US has similar legal requirements but those are not advertised as a "feature"...
it is illegal to sell non rohs compliant electronics in europe (if they were manufactured... after july 1st 2006)... and it is illegal to sell electronics in the USA that don't meet similar standards.
Now between 2003 and 2006 companies COULD start selling rohs compliant parts early (since the rohs was signed into law in 03, requiring all electronics meet it by 06).
As an aside, if you DO find a REALLY old part that was made before rohs (and not just a case where the manufacturer did not splatter rohs all over the case), buying it is not gonna encourage pollution, in fact if nobody buys it just ends up in a landfill, if YOU buy it you can be responsible and bring it to your local hazardous materials disposal center (one in every town) when you are done with it.
You might as well look for "murder free" motherboards while you are it.