The problem with this, as I see it, is that adding any or all of those has some very serious setting implications. A law limiting purchasing? Now you need a (reasonably) stable state in order to enact those laws, and every state has to do the same, or else one state will become awash in magic items and start selling to their neighbours.
Laws like that are very common in the real world, even today. Try buying a bulletproof vest (legally) without proof you're a policeman. Try buying from the PX without proof of being a serviceman or dependent.
Back in the times most similar to those typical of a FRPG, carrying a weapon bigger than a knife was something that was pretty tightly controlled, even if it is something most games gloss over.
Limited makers carries all sorts of setting implications - how is that determined?
In most feudal societies, who could legally produce certain items- especially arms, armor, siege weaponry and any other technologies deemed to be important to the well being of the state- would be controlled by royal edicts. Produce something without the right seal, and you could face ruinous fines, exile, or in extreme cases, the death penalty.
Similarly, NON-vital trade secrets- such as a cheaper way to create porcelain, or the fine glass working secrets of Murano- were guarded no less violently by trade guilds or even individual makers.
In such a society, the creation secrets of magic items of all kinds would be guarded with equal or greater diligence and force. Even
magical force.
Hell- some creators may be magically compelled to sell only to persons bearing a certain mark.
what is the point of having makers in the setting that won't sell to the PC's?
Introducing them to the grey market, the black market, the Thieve's Guild or even doing without.
(I spent many months of campaigning trying to get a masterwork Dire Pick made for my PC in a RttToEE campaign. Never got it- the locals weren't up to it. And that was far more common an item than anything magical.)
how are the PC's going to go where the items are being sold? how much of a time sink is this? etc.
Those are campaign/DMing issues.
The distribution thing is also an issue. "genuinely new and undiscovered" is going to have serious setting implications and destabilization effects. If State A can make magic items, then all of State A's neighbours are going to want in on that.
Which is why those secrets get protected with the full force of Royal authority.
Geographically isolated only lasts until the players figure out how to change the geography.
Congrats- your setting just became more dynamic! That's a good thing.
Great if you run only one campaign in that setting, but, again, makes the next campaign a bit tricky.
Who runs all of their settings from the same starting point? Why should my campaigns all be like FR, when there is Greyhawk, Spelljammer, Eberron, and DarkSun? Not to mention Middle Earth, Nehwon, Earthsea, Hyborea, Melnibone, and stuff I homebrewed? Or kitchen sink settings?
One of the biggest complaints about 3e was the magic walmart and fungible magic items.
This is one more place where your experiences and mine differ.
I participated in any number of "Monty Haul" games- as player and DM- in AD&D and 2Ed. No magic walmart needed when the DM is handing out soulswords like valentines candy. But I was a young teen.
In my late teens forward, from the end of 2Ed through 4th, magic items were treated as normal goods, night and sold. But NEVER was there a magic walmart. At best, there was a specialist in making (whatever) who had a few things for sale, sometimes for the stated prices, sometimes less, sometimes more.
Sometimes, we role played it out. Other times, each player submitted a list, and the DM would tell them what they were able to find, and at what price. Nobody EVER got everything they asked for, unless they set their sights very, very low.
IOW, the explosion of availability of magic items ISN'T system specific, it is a playstyle thing.
