Here are some useful links to find internships 

1) Career Services WolfWorks - this is for students and alumni for internship and full-time positions. 

2) ACS Careers - Has a link called "Find An Internship" keeps a running tab of chemistry internships, Co-Ops, and REUs all over the country. 

3) REU Sites: Chemistry - This is a list of the active chemistry division funded REU sites (Sites with active NSF awards). 

4) Internships for Undergraduate Chemistry Students - Get real-world experience through internships and summer research programs to gain the professional edge.

5) Federal Opportunties for Undergraduate Students - Federally-sponsored opportunities for undergraduate students and undergraduate programs in science, technology, engineering, and mathematics (STEM) areas. These opportunities range from scholarships and research internships that undergraduate students can apply to directly to funding opportunities for academic institutions to establish innovative undergraduate training programs.