I'm a big fan of Boldini. I have a 2 volume copy of the Boldini Catalogue General (in French) which cost $150. It was not easy to find. You have to search out the used book dealers such as
www.abebooks.com . Both Amazon and Barnes & Noble can hunt down used books. I recommend them. Also try
www.alibri.com.
:idea: On a brighter note, a Catalogue Raisonne was recently published in Europe (this year I believe). I tried to locate a copy but could not. I believe it is mostly in color--my book is about 50/50. You could also try contacting the Boldini museum in Paris. They have a website but I don't remember the url.