There are different kinds, at least two that I am aware of are gudbrandsdalsost (from the Gudbrand valley) which is a mix of cow and goat milk (and is probably more palatable for the average person) and ekte geitost, all goat milk, has a little more "character", I'd say because I lack the vocabulary for describing tastes well. The best chance of finding it in the US is probably under the name "Ski Queen" which Norwegian company Tine uses for its exported product. I'd try Whole Foods or a local cheesemonger (they might do a special order?), and if those yield no results, there appear to be a couple vendors on Amazon that ship it with an ice pack (the price is a bit steep if you're only mildly curious). Edit: A little goes a long way. An ostehøvel cuts quite a thin slice from a block.
It's whey that's been reduced to gravy consistency and then cooled, with cream maybe added near the end of the reduction process to make it smooth.
I wish I could post pictures. I took a photo this summer of all the Tine (manufacturer) brunost available in the supermarket. They were:
Innherred (Brunost – mørk og søt); Geitost* (Ekte – rik og kraftig); Junior (Fløtemysost – lys og mild); Gudbrandsdalsost (Original – G35); Fløtemysost (Lett – 16% fett); Fløtemysost (Original); Misvær (Brunost – lys og mild).
Prices ranged from 130-170 NOK.
*My favourite cheese of ALL time.