One word of (unsolicited) advice. If you do use white spacer material, put a different colour next to the blade itself, then the white next to the scales. If the white is next to the blade, it will grey up every time. Looks pretty bad. When I have the need to use white, I put a very thin black spacer material between it and the blade. Problem solved. If the scales are a light colour, I sandwich the white between two thin black pieces.
Any of the knifemaker supply houses carry it.
K&G and Texas Knifemaker's Supply have it where you can download their catalogs.
C Wilkins