Based on what you describe, it sounds like you really want a 1/4 male NPT to 1/2 hose barb fitting. Whatever. I always recommend
www.mcmaster.com for stuff like this. Shipping costs are never listed, but are very reasonable (standard UPS charge, not marked-up). Only real problem is that it's tough to buy single fittings. If you need 25, you'd be all set.
Anyway, from their main page pipe and tubing fittings are in the upper-left group of items.