Brunost has been made in Norway for centuries and like most traditional Norwegian food it harks back to a time when Norway was a relatively poor country. Usually the whey is thought of as a by-product of cheesemaking proper, and not for human consumption on its own (ricotta being the notable exception), but the wily Norwegians found good use for it, and it must have provided another welcome source of protein.
Although eaten in Sweden, it’s only really the Norwegians that have truly embraced it and regard it as part of their culinary heritage in a semi-fanatical way – in much the same manner a Brit might regard Marmite. There’s even a group on Facebook singing the delights of brown cheese with strawberry jam (not as bad as it sounds incidentally).
Norwegian Seaman's church, where they have an annual Norwegian food festival around Christmas time. In the U.S., I was able to track down the Ski Queen brand of brunost at the local branch of Whole Foods, which is made by Tine, Norway's dairy monopoly.