Buywake.com has what you need. Rainbow pro locks, 12 bucks for a set, here's the link: http://www.buywake.com/catalog/detail.lasso?cat=6&man=Rainbow&sku=AM_1183
In a pinch, I'm sure you could get by with flat head machine bolts from the hardware store, combined with wide-diameter washers. Make sure you get stainless steel, and take your board/bindings to the store to make sure you get the right ones. I would go with the Rainbows.