Best Way To Find Recent Stamp With Color Error

I apologize if I'm posting this in the wrong place.

I have a small collection of used stamps from the Italy 1998-2004 "Women in Art" series with differing color variations.

I would love to find an example with the head in green, shown below, and am wondering what my best chances might be for locating a single stamp. I regularly browse delcampe, hipstamp, ebay... but would love to know about other possibilities.

There has been a lot of fun and games going on with printing of Italy stamps for the last few years . I discount all these as printer waste .