が is used with あるmost times except in cases of ありません, in which case you can use the particle は.
Isn't this supposed to be が not は
は is technically not wrong, but が is better, because of regularity in questions about a subjects existence. As noted above, が is more common in front of ある.
^ but は is used when introducing a subject
It might help to remember that は throws the emphasis onto what precedes it and "ga" throws the emphasis in the other direction.