The webCASPAR site has National Science Foundation data on the number of alumni who complete PhDs in various disciplines.
https://ncsesdata.nsf.gov/webcaspar/index.jsp?subHeader=WebCASPARHome
For example, the following are the numbers of alumni from several Pennsylvania LACs who earned PhDs in economics from 2003-2010:
7 Bryn Mawr
6 F&M
5 Haverford
5 Dickinson
Here are the numbers I found for mathematics & statistics:
14 Bryn Mawr
14 Haverford
8 F&M
2 Dickinson
1 Muhlenberg
Some individual college sites have data on their recent graduates’ activities.
Try Googling for “after graduation [COLLEGE NAME]”, or some such.