Spells generally only work on for the turn they're played (i.e. - immediately used, and their effects don't 'last for a few turns'). Perhaps it can just be a 'one-turn' deal, where you can consume all Freeze effects to generate the corresponding amount of Ice Bolts | Ice Lances in your hand once you play it? It'll be like a really specific version of Fractal, dependent on how many creatures are frozen on the field.
Also, you could have it so that as a permanent that generates an Ice Lance in your hand whenever a creature is frozen (Permanent effect), but that could get really ridiculous... ^^: