You cannot feed spent grain as a sole diet to a calf. You will have to provide forage (hay) if your grass runs short. Another option might be alfalfa cubes or pellets. They're available in some areas and are a simple way to feed forage. You start getting into hay handling and you end up needing more equipment unless you use idiot cubes.
I would look for a dairy calf but a warning, milk replacer is EXPENSIVE. I would cruise craigslist and contact the local dairies direct as well. If you can get a little older calf, you're better off (less expensive milk replacer and closer to weaning).
Pellets will double your hay costs. Around here, hay is going for about $200/ton now. Pellets are $400 or more.
