Hmm... I can try that but these professors go through hundreds of students a semester, so I have doubts that they would remember who I am just from office hours. I could maybe try my freshman chem prof since I got an A+ in his class, or would that be too long ago? What about letters from classes that aren't the giant weeder courses (i.e. Orgo, Bio, Physics)? At my school we have these biology electives that you're required to take as part of the biology major, and the classes tend to be smaller. I already have my research PI and non-science letters sorted out, but I didn't expect a science LOR to be the hardest to find!