In addition to Torreson,
Marine Diesel Direct,(http://www.torresen.com/), I've also used "Marine Parts" at the link below for some parts for my Yanmar 2GM20F. But before you buy a new or rebuilt raw water pump, which will be somewhat expensive, is it possible that all you need is to rebuild the seals in your existing pump? If so, rebuild kits are much cheaper and it's not a hard job.