OT: Any good acrylic primers to airbrush...?

You won't have any problems spraying different mediums through your airbrush as long as you clean it properly between uses.

If you just want a base coat that doesn't need to fill gaps or get a heavy sanding, you can shoot Tamiya acrylic neutral grey. It isn't exactly a "primer" in the traditional sense, but it works nicely as a neutral base coat.

Glenn