I don't like the black markings in the tip. Still, whatever the condition you should treat it more or less the sane: keep it warm and dry for a while until everything is fully callused over. If anything starts oozing or collapsing into mush then you may have to start chopping. Or call in that lifetime guarantee
There are many online sources for healthy Trichocereus as well as other cacti, but very often they are not the large (pieces of) plants that "shamanic" shops are selling.
Miles 2 Go lists a couple of species but they are fairly small.
Mesa Garden has many more but I think they will be even smaller. Shipping large live columnars about in good condition is not very practical.
I do recommend that serious growers avoid places selling plants mainly to be eaten Tey will eventually attract attention from bored lawmakers and then more cacti will become illegal to possess.
The seeds should be fun. These things are fast growing although that might only be a few inches a year at first.