Headers will not buy you much even if available. A custom header fabricator could probably weld some up for you, but the WK2 engine compartment is tight. Every once in awhile here a group tries to get together for a group buy, but it doesn't seem to materialize as I'm guessing headers for the 5.7 are not that feasible. There was someone trying to replace the 5.7 with a 6.4 but never could get the computer to work properly.
By the way, "performance" parts for 2011-2013 should fit the 2014 physically. The 2014 has a different transmission and different control bus, but is otherwise the same. IMHO, beside a tuner and some brake, tire, and suspension bits, there is no real performance upgrades available for the WK2, but there are several that will make the WK2 sound better (e.g CAIs and Cat Backs)
2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6, 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac