Whiskies with a high percentage of rye are actually fairly difficult to produce. The enzymes in common use for breaking corn starches down into sugars don't work well on rye, and the typical result is incomplete conversion, a gummy mess, clogged machinery, and a lot of extra cleaning and maintenance. Producing pure rye whisky efficiently requires special strains of fungi, etc.. For this reason and the relatively low demand for pure rye, there are very few producers out there. A mixture containing a small percentage of rye and a larger proportion of corn or other grains is much easier to work with, but a lot of whisky producers simply buy rye whisky and blend it it with their own whisky.
Other "producers" buy rye whisky and sell it unaltered. For example, Whistlepig rye and Masterson's Rye, whose websites both make it sound like they produce these products, are made from rye shipped South from Alberta distillers. Alberta Distillers supplies a significant percentage of the rye used in premium "artisanal" rye whiskies "made" in the U.S. as well as for flavoring various other blended whiskies. Oddly enough, their own whiskies (Alberta Premium and Alberta Springs) aren't typically sold South of the border.
Every few years Alberta Distillers puts out an extremely limited bottling. The last one was a 30-year-old 100% rye priced at a truly bizarre $50 a bottle. It literally sold out before hitting shelves. I had to ask a liquor store manager to set aside a bottle for me, and when I picked it up he said they weren't even bothering to put the stuff on shelves. People remembered the 25-year old bottling from 5 years previous and the bottles were all spoken for while still in the crate. The stuff was amazing. They could have sold it for $500 a bottle and it would have offered better value than any scotch priced that high (Honestly, a lot of scotches priced that high aren't very good at all). If you happen to be in Canada when the 35-year-old edition comes out...