Unfortunately, most places only accept 4th year students for visiting rotations (which really stinks when you're a third year trying to find electives). I am doing both of my electives this year at community hospitals where they are more lenient with letting people rotate. The best option is to contact the hospitals where you're interested in rotations. Sometimes you can find exceptions to the rules.
Radiology, even though it can be somewhat boring (especially at a non-interventional site), is a good way to brush up on anatomy again and helps you out tremendously in the future. Even if the pathology is limited where you rotate, you can still get a method in your head of how to read the more common studies (CTs of the head, neck & chest, CXRs, MRIs of the brain, knee, spine, U/S of abdomen & pelvis).