Sorry I didn't see your question before Sat. I just found this forum. I have a cow although she is only part dairy, but have milking goats and one thought I had was to make sure you can handle her. My friend bought a yearling cow to milk and she never did milk her because she couldn't handle her. Also I would call my local ag extention agent to find out about immunizations she should have.
Good Luck! Let us know how the hunt goes.

Our friends get their cows really young so they can be brought up tame. Their kids go bring the cow in for milking every night and during the day she mostly is tied out eating up tall grass. Kind of like a self motivating lawn mower.

They generally get a Jersy cross of some sort since they want rich milk instead of quantity of milk.