To open a campaign map from any campaign you find :
- Open World Editor, open Campaign Editor.
- In the first tap, in the right side, there is a list , click '+' symbol and every map in every chapter of the campaign will appear.
- Right-Click and export the map you want.
- Now there are two solutions to fetch everything you want from that map :
#1 - Open it by regular Editor.
#2 - Use MPQ Editor, open the map , and everything will appear ( uploads too ).
If you didn't see the uploads you want, just go to Campaign Import Editor as @Veritas said.