Both concepts are interesting. If I remember correctly in the AD&D setting "Dragonlance" there also was only a little of magic left in the world what made it interesting in its own way.

One possibility of making magic items sprecial could be to give them some kind of "charges". Then they are burnt out or they can be recharged with great effort, for example by having to make a long journey to their creators or by fulfilling a special quest.

If you have the right group it could also be interesting to let using magic items make them pay a price. This could be a reduced attribute for a couple of hours/days or something similar.

I think even in a world with rich sources of magic it would still not be possible to buy every item existing in the local shop. If players want to buy a special magic item they have to do research where this kind of item could be offered. Perhaps some items are only made in a small region. Or they cannot be produced anymore and are only given away to members of a specific group. Another possibility could be do spread rumors that a magic item will be on some kind of auction, a nice possibility for some adventure hooks.