The following link is an a capella blog with lists of a capella groups from colleges everywhere. It is sorted by location so you can find Amherst’s groups on the first two pages with links to many of the groups’ web pages.
The groups that I see listed are:
Route 9 - http://route9.webs.com/
Sabrinas - link broken
Sh’ma Cappella - no link
Terras Irradient - https://www.amherst.edu/campuslife/studentgroups/terras_irradient
Zumbyes - http://www3.amherst.edu/~zumbyes/
Bluestockings - http://www3.amherst.edu/~bluesox/
DQ - http://www.thedq.org/
Madrigals - http://www3.amherst.edu/~madrigal/
In addition there was Instrumentally Challenged (no link) which looks like it is open to the Five Colleges.
Amherst College is known as The Singing College - perhaps others can tell you more about why.
Take a look at this post for more:
http://talk.collegeconfidential.com/amherst-college/626226-is-amherst-really-the-singing-college.html