I have a RS Revelation that needs a replacement air cap. where can i get one ?
Can't see just the cap with a quick look, but you could always use a normal schrader valve cover.
Universal Cycles -- Rock Shox 32mm Air Top Cap Assembly
ebay might be your best bet:
2013 Rock Shox Larger Volume Air Cap | eBay
Rolling on 29", 650b, 8.3" and 23mm
It's part of some service kits as well.
Revelation Service Kit