Actually, to be able to specialize in your undergrad is actually kind of rare. Most programs will just have a degree in psychology, you can then take a bunch of social psychology.
This is the list I found off Princeton review American Military University American Public University Augsburg College Bard College Bard College at Simon's Rock Bennington College Bethany College (WV) Burlington College Clarion University of PA Eastern Nazarene College Eureka College Fisk University Harvard College Keene State College Maryville University of Saint Louis Mid-America Christian University Moravian College Northwest Missouri State University Park University Prescott College San Francisco State University State University of New York at Albany Suffolk University Temple University Tennessee State University
If you'd like specifics, try collegeboard.com and click "Find Your Match." Across the top a list of criteria will show up, and from there you can type in "Social Psychology," click "go," and once you follow the directions, just hit "see results" if that's all your criteria for colleges.
most colleges off that. almost any college that has psychology programs will have social psychology as an option.