1. Keep looking, and looking, and looking! Start early, and explore often. What are you interested in? What kinds of industries would you like to work for? What areas of study keep you up at night (in a good way) that you'd like to pursue in grad school? Do you want to transition from chemistry to chemical engineering, biotech, or a related field? An internship can help with all of these questions. But only if you have your eyes open. As one recent grad put it...
"Don't be picky and apply to everything. When I was applying for internships I applied to a ton of REUs (starting my freshman year)"
2. Explore solid job sites. These include chemistry.org (search on "internships"), doe.gov (SULI program), inl.gov (local INL internships), local, regional, and national industry websites, the REU program at http://www.nsf.gov/crssprgm/reu/reu_search.jsp, regional and national universities (find their chemistry webpage and look around). Also, check the bulletin boards around the chemistry department, there's always new material going up.
3. Ask returned students about their internships. Where did you go? How did you find your internship? What inspired you to look there? What did you learn the most? What would you have done differently? Learn from your peers, many of them were in the same hunt you are now, and not very long ago.
4. Use contacts and networks. Know someone from your ward? A family acquaintance? Parent of a friend? Former roommate who just hired on? They may know of opportunities you're looking for.
5. Build some experience into your resume. Participate in a mentored research project with one of the chemistry department faculty. Ask around; research is happening right nowin the following areas: