the original bridge on the G3 is similar to the stamped metal bridge that Fender uses, so you might be able to find some that will fit that's not original. you can find more info about the G3 at gibsonbass.com
also, there's a lot of places that will make the pickguard for you if you have a tracing or the original. check around.
here's a place that has a good assortment of screws
http://www.mojomusicalsupply.com/index.asp
let's see some pics when you get it done!