They grow to about 12-14", so they would prefer a large tank towards adulthood (125g). They are a peaceful schooling fish, actually in the tetra family. They will usually only accept live foods, but you may have the skill to wean them on to prepared, good luck
I sometimes sell them, but I have none in stock right now.. You might want to try other online sellers, or request them at your LFS. They sometimes call them 'needlenose gars, rocket gars, hydro gars', or other various names, but you also get alot of other needlefish under those common names as well.