You're talking about the "shrader valve". I typically replace those whenever doing a major service on the a/c system. It's like a dollar generally, but unfortunately Honda will only sell the entire hose with the shrader valve inside. Personally, if my school didn't have any in the shop, I'd pick up the shrader valves from Toyota myself and use them.

Two things though, lube the replacement valve with mineral oil (not PAG oil), don't saturate it, just simply lube it. Second, you'll need a shrader valve removal tool.

You know you'll need to evacuate your system before hand and you'll also have to have your system redone under a vaccum again before you put in the R-134a back in. (Moisture/air in a/c system = bad for system.)

If you're sure it's your shrader valve then more props to you, but I would inject dye in your a/c system to more accurately pin point the leak.