You could always try using a traditional goose quill, but it may just be that you have the microphone a bit too close.  As IvanB mentioned, food containers can be a good source of material; I used to make them out of margarine lids, but only when I was broke.  The pick needs to flex easily as you strum, and you might also try holding it nearer to the top; it'll break sooner, but the sound should be more delicate.  That "ker-pluck" sound can be useful if you're playing dance music, mind.

Malcolm