What spheres would a mage need to be able to indefinitely provide an unlimited supply of blood to a vampire?
Matter 3 can transmute water into blood.
Alter Form: Allows a mage to change the essential nature of a Mattern Pattern, changing its form or even compressing or expanding certain elements of its material properties (i.e. lead to fog). (MtA)
If your storyteller interprets the Vampire sourcebook to mean that blood in and of itself is inert and lacking vitae to sustain a vampire, then the mage can use Prime 2 to instill the blood with a pattern of Life using quintessence.
All of these are the Prime 2 capabilities needed to do so:
Fuel Pattern: Allows the mage to store small amounts of Quintessence in an object. (MtA)
Enchant Patterns: Allows the mage to enchant the natural properties of a Pattern by tapping into its Quintessence, allowing it to interact with ephemeral objects. (MtA)
Create Pattern: In conjecture with other Spheres, the mage can create a simple Pattern out of thin air, by diverging the flow of Quintessence in the Tellurian into the new form he wants to create. (MtA 20 Anniversary ed)