You can find several companies online that will sell certified turfgrass seed but it will most likely be fairly expensive.  You may also be able to purchase seed from a commercial turfgrass distributor in your area, or in Portland.  FYI most seed companies in Oregon do not sell direct to consumers so you will have to purchase through a distributor (online or local).  I would highly recommend purchasing certified seed (blue tag), this will ensure minimal weed seed or other crop in your bag of seed.  You never know what is in the uncertified seed.

As for the seeding rate, we typically recommend 2-3 lbs/1,000 sq ft of pure live seed for Kentucky bluegrass and 5-7 lb/1,000 sq ft of Perennial ryegrass.  The actual rate will depend on the percentage of each species in the blend (bluegrass has much smaller seed), but in general we recommend around 5 lb/1,000 sq ft for this blend.  This means you would need about 435 lbs of seed for the 2 acre area.  I would order at least 10-20% extra to make sure you have enough seed.