Buying in smaller quantities in DC? It takes me too long to finish 12 oz bags

Are there any place in the DC area that let you buy in smaller quantities than 12 ounces? I would like to get into single origin coffee and would like to sample as many as I can over a short period of time. However, it can sometimes take me 2-4 weeks to finish a single bag, and I'd hate to get stuck with a big bag of beans I don't enjoy.