Search in the tree of resource bundle keys and values in Branding editor is possible, but it is not obvious immediately.
User needs to right-click the root node (Resource Bundles node), invoke Show all bundle keys action, and then start typing what she is searching for. A regular tree view's quick search field appears at the bottom of the window, where the user specifies the search string. Pressing F3 repeatedly cycles through occurences of the search string in the tree.
Adding a permanently visible Search field in the window would help significantly.
Integrated into 'main-golden', will be available in build *201004210200* on http://bits.netbeans.org/dev/nightly/ (upload may still be in progress)
User: Antonin Nebuzelsky <email@example.com>
Log: #184336 - Searching through Resource Bundles in Branding editor is too hidden