Aprille, there's a great site online that carries almost everything Airbrush.
They also carry the bottles and Caps like the ones you have.
Airbrush Supplies
As for the overspray, you might try checking you're air pressure. Depending on the surface you are spraying you need to adjust your air pressure accordingly. I actually add air pressure when I'm doing Tye-Dye on plexiglass to give the colors a more softer edge and to blend the design together a little bit.
I've added some pics below to show what I mean. Please forgive the reflections, I'm not accomplished of a photographer. Also, the door was done using masking to avoid the overspray.
I hopr this helps some.