Are other needle/tip sizes available?

Yes, there are various size tips that are available.  

Included with the sprayer:

• 1.5mm-Fine finish atomization.  Stains, water base finishes, and polyurethane.   

Available separately:

• 1.0mm-Fine finish atomization.  Sealers, varnish, and water base finishes. 
• 2.0mm-Fine finish atomization.  Latex paint, chalk paint, milk paint, varnishes, polyurethane, and oil based paints.
• 2.5mm-Medium finish atomization.  Latex paint, chalk paint, and milk paint.