The map file for Rexxar Campaign was located in "War3xLocal.mpq" (for Act 1) and "War3Patch.mpq", but when Blizzard merged both ROC and TFT clients starting in 1.28, it was stored in "War3x.mpq" file instead for all 3 Acts (along with the 4 main campaigns for TFT).
If you want to open the "War3Patch.mpq" file (for 1.26/1.27), you'll probably need the Listfile so that when you open that file it doesn't show weird names.
As a bonus, if you want to identify the sub-map names for Act 2 (it's a bit confusing due to the map having 5 submaps for main quest and 4 submaps with dungeon monsters), here's a correct one:
1.OrcX02_02.w3x (Coastal Base - Infiltrate Theramore Quest).
2.OrcX02_03.w3x (Theramore City - Escape Theramore Quest).
3.OrcX02_04.w3x (Dustwallow Marsh - Ogre Quest).
4.OrcX02_05.w3x (Mulgore - Tauren Quest).
5.OrcX02_06.w3x (Tidefury Cove - First Blood Quest).
6.OrcX02_07.w3x (Tombs of the Ancients).
7.OrcX02_08.w3x (Den of the Lost).
8.OrcX02_09.w3x (Magistrate Temple).
9.OrcX02_10.w3x (Outland Arena).
Interesting thing is: Editor throws an error like this if you attempt to open each submaps for Act 2 (My version is 1.29.2):