Typically people don't want Arcane equips in Marvel Machine because it's seen as selling power; pay to win. A free-to-play user could, in theory get themselves through Lucid just enough to obtain their own weapon, but putting the equips in Marvel is seen as paying for the best equips in the game. It's also seen as a bad move towards the people who run Lucid, since they worked so hard only to obtain the equips only to have them released to anyone who pays Nexon for them.
Personally, I think funding yourself off Marvel (or any cash box like philosopher books) is stupid, since most likely you'll just wind up with an inventory full of hair coupons and a bunch of scrolls you don't want, but I certainly understand what's pay-to-win about releasing Arcane Umbra equips in Marvel.
If you see someone selling Arcane weapons for real money you should report them in-game or via a ticket; particularly since the number of legit weapons is currently in a grey area and illegitimate weapons could potentially exist.