Upgrading Mac Pro 1,1 CPU

Hi.

I own an early mac pro 1,1. It has a dual core 2.4ghz or something there abouts. Id like to upgrade the cpu to a quad core or better. Ideally 2 chips. (8 core +) What intel processors will work well in this model mac pro? Can someone please give me a list of upgrade options? also does apple sell them? if not what would be the best sites to research and buy from? Im in australia.