Your local hobby shop or craft store should carry a good line of fabric acrylic paints. They are fairly easy to work with because they thin with water and most of the clean up can be done with water. The pigment must be thinned to the consistency of heavy cream, in order to flow properly from the nozzle. When dry, the pigment is permanent and NOT water soluable. However, be aware that, since the pigment is sprayed on in a very thin layer, the design will not be as permanent as a good, silk screened shirt.

Also, be sure to filter out your inks, each day, before filling the spray bottles. You want to make sure that no solid chunks are in the paint because they WILL clog up the spray nozzles. I found that silk screen fabric works great for this. Buy a yard or so of this material. You only use a couple of square inches each time you do this, so, it will last a long time.

I used to airbrush tee shirts at craft fairs. Many designs were requested often, so I cut some stencils out of manilla file folders. They were sturdy enough to re use several times. I used a light application of spray adhesive to stick them to the shirt. The craft stores also should carry a cardboard shirt form, which, when tucked into the tee, would provide a stable backing on which to work.

For finer, one-time custom designs, ther is a material called "frisket," which is a very thin, peel off material, from which I cut out stencil designs. I used an Exacto knife to cut out the thin material from the plastic backing, then, I could peel off the stencil and re apply it to the shirt. Provided a nice, hard edge, when needed and was great for very fine, detailed lines. Multiple colors became much more controllable with this material. Unfortunately, frisket was not particularly reusable on fabric.