it's not really any more difficult than any other area. you just apply for a job by sending in a resume.. however few nuclear labs have interns, according to my boss (supposedly only a handful of our 100+ locations have interns). you also have to work at 1am or 2am during the school year, which can be a pain.. but well worth it in the end..
dont know much about compounding pharmacies.. but again there are only maybe a handful of compounding pharmacies in a given metro area, compared to hundreds of retail locations.
Work on your resume. I feel like my hospital experience helped me to get my nuclear job. That may be a good place to start since hospital internships seem far more numerous than nuclear or compounding... And the compounding experience you get at a hospital will be far more extensive than working in retail ( i think,.. can anyone tell me if retail does much compounding?)