If I say "there's plenty of magic in the world... but it isnt bought or sold, sorry" and a player complains (and from the original post its an ongoing complaint by a minority of the gaming group)... thats a campaign decision.
I don't understand how in a world where something is plentiful that no one would ever think to buy or sell it. "So valuable that it will never be sold" and "plentiful" are mutually exclusive, in my book. And how do the players come across these plentiful magic items? If they trade gems/items/services for magic items, that's still buying and selling them. Or maybe they're so powerful and valuable that they're all lying around in a dungeon somewhere.
But then again, this is a fantasy game subject to the player's/DM's tastes. Maybe in a fantasy setting where orcs rampage and elves frolic, free markets and daring entrepreneurs don't develop. "What do we do with these extra magic items we have, Berk?" "Maybe we should hide them in a dungeon for the next group of adventurers to find, Cutter!"
If I told my players that "there's plenty of magic in the world... but it isnt bought or sold, sorry" they'd most likely go to the library or sage's guild, find out who owns these magic items, and go kill them for their valuable magic items. Not the kind of heroic game I want to run.
IMO, a reasonable and mature player who is left with the choices of 1) play in a DM's game that isn't suited to his specific gaming tastes; or 2) don't play at all; accepts his situation and makes a committed decision between those two choices. As I said before, only a child (or an entirely too child-like adult) returns to a friends game week after week demanding that the game be changed to suit him, despite clear indications that change will not happen and his constant complaining about it is unwelcome
Hmmm, where I come from mature adults compromise, because we all understand we'll never get everything we want. Only children think they should always get their way.
So I am able to appease my players by allowing them to buy or trade for items from time to time (up until now it's just been minor items as they have just hit the 7th level mark), but I retain control by limiting what they have access to.