The Cummer Museum in Jacksonville has a couple stellar Bouguereau's....I can count the times art has made tears in my eyes. That is one of them.
The easiest thing to do is go to www.artrenewal.org and look through the paintings. It shows what collection they are in. Otherwise Fronia Wissman's Bouguereau book will say as well.
The Sargents in Boston are gorgeous.
LA has a few Sargents, LACMA and the Huntington Library. SF Legion of honor has a couple bouguereaus. Detroit...Mnpls...lots of places.
"Join us in London for the upcoming ConceptArt.Org Workshop. More details at workshop.conceptart.org .