Just take the "decanter of endless water" and modify. Like so:
Nipple Shield of Evermilk: If the command word spoken is spoken while the nipple ring is worn, an amount of fresh milk pours out. Separate command words determine the type as well as the volume and velocity.
• “Stream” pours out 1 gallon per round.
• “Fountain” produces a 5-foot-long stream at 5 gallons per round.
• “Geyser” produces a 20-foot-long, 1-foot-wide stream at 30 gallons per round.
The geyser effect causes considerable back pressure, requiring the holder to make a DC 12 Strength check to avoid being knocked down. The force of the geyser deals 1d4 points of damage but can only affect one target per round. The command word must be spoken to stop it.
Moderate transmutation; CL 9th; Craft Wondrous Item, create food and water; Price 9,000 gp;Weight 1 lb.