Boeing seems to be moving towards another tanker scuffle. This time they are apparently trying to prevent IAI from building any critical mass in the tanker business.
There are three primary places you can buy an aerial refueling tanker: Airbus, Boeing, and IAI. Russia and China also are options but are not as a common as Boeing and Airbus. Boeing was not the inventor of the aerial tanker business. Airbus is a much more recent participant and has done exceptionally well and beaten Boeing several times with its A330 MRTT in competitions.