Looks like Weberbauerocereus. From the ones I have seen the epidermis seems to have a distinctive granular texture, hard to see in a photo and is hard to explain to others unless actually seeing the plants or comparing them to other smooth textured Cerei epidermis.
Regarding rarity, this varies according to country and time. There were a lot of Weberbauerocereus grown from seed when Friedrich Ritter was collecting in habitat in the 1960's and sold under FR numbers by his sister Frau Winter in her German seed list. She marketed his habitat seed for him in Europe and no doubt sold to the the USA and Australia.
As said before, if a species does not have a wide collectors market in your country the nurserymen do not bother to propagate it. Therefore plants that were once initially common then become rare. Certainly with plants that have to be larger to flower and are not really attractively spined, or needing to be very woolly to appeal to a general non specialist public market. With some of these less marketable species they are often still available in seed lists, but you need to raise them yourself since the nurserymen will no longer bother.
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