Just for some clarification, the word "Warlock" comes from the Anglo-Saxon word "Waerloga" meaning "traitor" or "oathbreaker". If is a term largely used by Hollywood and by fiction writers, but not for actual magic users.
If one is talking about a male Witch, then the term should simply be Witch.
John Constantine is a comic book character from Marvel Comics. Comic books are not a reliable resource when it comes to understanding real magic and real magic users.
Well then I guess Lamashtu isn't real? Nor is Naamah ? Durgia? Maybe Lilith? I'd argue your point but some of it is fake. But the murr against spirits isn't real? Nor is blood magic or the binding of spirits? Maybe giving away your soul or replacing your own with Pazuzu? I'm just wondering here. I guess they're real, but some things portray it differently than others. Your points are valid but I have a tiny feeling at least SOME of them are real, I hope you know what I am getting at here. I hope I don't come off as rude, luv.
There may be aspects of real practice, demons and deities in John Constantine comics and the show, but that does not mean that what he undertakes is real magick, it is simply inspired by for effect.
In regards to items for spells, no item is required, you can do without the difficult to find herbs such as wolfsbane, you can actually undertake successful spell work without any items at all. If you are determined to use herbs, etc, in your workings you will likely have to go online to find the more unusual herbs, unless you have a herbalist store or new age store near you that stocks it.