buy one from Goodsprings, or you can pick one up from a greenhouse in the Sharecroppers compound. (I recommend Goodsprings, as you need all the loot you can get early on, and graverobbing is a good way of doing it)
There is also one at Goodsprings the Source ( I think it's called) that if I remember, is full condition. I think it's leaning against one of those concrete troughs.