Some of the other tribes that have elevated levels of R1b are in northwestern Canada and in some cases are Dene. Plus, there are apparently high rates of R1b among the Dene who migrated into the southern U.S. about 400 years ago (the Navaho and Apache). Of course, there are other tribes in eastern and central North America that have significant amounts of R1b but they also have significant amounts of other "European" Y haplotypes and a history of heavy intermarriage with whites, so I wouldn't make too much of the R1b in those tribes - examples are MicMac, Quebec Cree and Cherokee. But it is odd that at least one Dene tribe has about 40% R1b and apparently no other "European" haplotypes and that the Ojibwe, which historical records would suggest have less admixture than some tribes, have nearly 80% R1b and only about 3% other "European" R1b. So the distribution might suggest that some group of Siberian R1b types, perhaps distant descendants of Mal"ta Boy's relatives, migrated across the Bering Straits after the initial peopling of the Americas and that some of them eventually settled around the Great Lakes, where there was copper to be had. Except that in order for that theory to work, the R1b should consist of unique subclades, and I'm not aware of anyone finding any so far.
At this point, I'd still be inclined to consider the possibility of sampling issues. If you look up the original studies, the number of samples is fairly small, and I don't know what the selection criteria were.