The only way to build a Jayhawk would be to use Italeri's SH-60 Sea Hawk with a Cobra Co Jayhawk Conversion set and a Hawkeye Decal Set, as there is no proper boxed kit. An excellent model can be built though from using the items above.
Kelly Quirk's stunning 1/48th USCG HH-60J;
http://www.hkngallery.org.uk/hkngallery.nsf/9e7858703c56bfb280256b960044cd7b/f46cf1bd5326b26e80256e86007efd39!OpenDocument
Cobra Co's homepage;
http://cobracompany.com/
HTH,