In addition to credit cards, you can cut scrapers from any plastic container like milk jugs, orange juice jugs, plastic buckets/tubs, etc. Cut some with curved surfaces to match the contour of the stock.
Semisane, first,I like your name. It applies to most of us. I like your idea of using an old milk jug or bottle. I was trying to think of any plastic card to use and I was drawing a blank.
Thanks.