A seller named "jimsgrips" on eBay used to sell some plastic/yellowish coloured ones for the M1929's and swiss-Interarms on eBay. He used to describe them as being a "micarta" material.
Here are his current listings...but none for what you need.
You might email him through eBay to see if he has any left...
http://search.ebay.com/_W0QQsassZjimsgrips