Find Familiar says:
Finally, when you cast a spell with a range of touch, your familiar can deliver the spell as if it had cast the spell. Your familiar must be within 100 feet of you, and it must use its reaction to deliver the spell when you cast it. If the spell requires an attack roll, you use your attack modifier for the roll.
And Magic Stone says:
You touch one to three pebbles and imbue them with magic. You or someone else can make a ranged spell attack with one of the pebbles by throwing it or hurling it with a sling.
I'm confident the familiar could touch the stones themselves, and deliver them to somebody else to use.
But does this spell "require" an attack?
If it does, then these both seem like exceptions to the general rule about Familiars not being able to attack. Otherwise can you read Magic Stone as 'granting' the spell attack, or does it not and only creatures that can attack can "make use of" the new spell attack option?
Either way can the familiar fling the stone and make an attack?