Get the radar gun from Housewares. It's in the Bistro behind a locked door. The audio log you get at the beginning of the level should have the code. Once you get this thing, make sure that the people you explode are near other splicers. When they blow up they'll take other splicers with them.
If you run out of splicers between the Electronics Area and where the bookstore/toy section is, you can cross the airlock. The action will re-spawn splicers. There should be three in the bistro basement, 2 in electronics when you exit the bistro, and then a few more back by the bookstore. Cross back and repeat as long as needed.
The Ammo is sold in the Circus of Value by the front door of the Electronics Department. Go nuts!