Try to go in person. We've been out for over 2 weeks, but it sounds like you still have them around on campus to even ask. Email is easy, but they'll take you more seriously if you approach it more seriously...since it is a serious thing. I was super worried about my letters because I'm post-bacc (so I had min. 280 max. 500 in all of my classes), my school is bigger than yours, and any non-science professors would be from over 5 years ago. I knew I was screwed without letters. We all need them. So I just nutted up and went for it and it worked out. Those who I assumed wouldn't do it, were more than happy to do it.
Think about how you want to ask before walking into their office. Wording can make a difference on how easy it is to say no. I even made a point not to dress like I was going to the beach or something. And don't whip anything out, but have some materials ready in case they ask or seem hesitant because they aren't even sure you were in their class. Having an easier time writing it is obviously attractive for them...especially since you're not total buddies with them. I gave a resume, unofficial transcript, personal statement and a short little 'about me' cover letter sort of thing with easy-to-read bullet points about me and sort of a pre-thank you for doing it. They don't get the real thank you until the follow through.
