Identify the subject

This is a command and has an implicit "you" as the subject:

[You] consider the latest idea from Warner Music Group, .... is the main clause.

which is rummaging, like the rest of the industry, for new sources of revenue  is a subordinate clause which modifies Warner Music Group. 

I believe it is correct as written.  However, in British English, Warner Music Group might be treated as a collective noun, in which case are rummaging would be used.