Harry Potter style gadget based limitation for magic?

[Calvin]

In GURPS the standard way to build a spellcaster that requires a staff/wand/orb/funny hat to be able to use their magic is with the suite of gadget based limitations. Now I'm not really concerned with how Breakable and Can Be Stolen break down because it's not really important. The limitation that matters here is Unique.

Now if you have Unique the consequences are very clear if for some reason your gadget is broken or lost.

But what if you don't have Unique?

I imagine a world sort of like the one from the Harry Potter novels. Barring a few very skilled casters (Who have spent the time to buy off their gadget based limitations) the majority of spellcasters require a wand to cast spells. Now in the novels the witches/wizards seem to have an easier time casting with their own wands, but the difference seems marginal (probably a -1 penalty, maybe -2 at most) and it's not as if replacement wands are hard to come by. That does have something to do with how many characters can be expected to be carrying wands, as in, all of them, but it demonstrates the concept I'm trying to get at here.

There's Unique [-25%], Not Unique [-0%] which isn't a real limitation but we'll call it one for now, but should there be a Really Not Unique [+x%] limitation?

To put it in GURPS terms, what if a Mage had a limitation on their Magery that required them to have a Staff in hand to be able to cast spells? The Staff in this context would be anything with the Staff enchantment cast upon it. Leaving aside the matter of whether a penalty is incurred for using someone else's Staff, what would this be worth as a modifier on the other gadget based limitations?

Now if this were intended for an actual Harry Potter campaign or one designed in that theme, where all characters can be expected to be spellcasters then I'd just say that's how magic works, assign no modifier, and call it a day. But if only one player in the party can be expected to use magic then the GM needs to balance the point costs of spellcasters against other play styles. Additionally, this is a limitation that has the player has the potential to buy off at a later date, so you might still want to assign a cost even in campaigns where this limitation applies to (nearly) everyone.

I'm tempted to say that such a modifier halves the value of any Gadget based limitation, whatever the combination of selected limitations might be. But on the other hand, such a limitation might be worth nothing. Maybe this is the default assumption in GURPS if you don't have Unique, but I doubt it. The description reads that replacement/repair "...might require significant time and effort (GM's decision)". And while "GM's decision" does suggest that this isn't nearly as complicated as I'm making it, I don't think that the original intent of not having Unique was for replacement/repair to be essentially trivial.

[Refplace]

Sounds like Accessibility, not gadget to me.

[Calvin]

Maybe, but pure Accessibility doesn't reflect the facts like the DR, how difficult it is to target in combat, or how difficult it is to wrest away from someone.

[Culture20]

Gadget implies that the power resides in the item, whereas HP style wand magic stems from the wizard and the item is just a conduit or catalyst.
Enchanted items would be gadgets; spells would seem better modeled by accessibility like “only while using a wand”. You could use the gadget rules to inform your choice of accessibility percentage, but gadget itself seems off for this.