You should be able to use the backtick operator to pass the output of find to rm, as so:

I think the -R option of rm only applies to directories, so I doubt that would be of any use here.

Actually, I'm kind of surprised that that find command works for you; I thought you'd at least have to specify the path to look for files. I usually give find a command something like this:

Which asks find to look in the current directory (".") for files with the extension m4p. find will recurse through any subdirectories by default, but I don't know if it will enter hidden directories; you might have to run the command something like:

So, in total, I'd probably have:

Check the output of the find command first, though, to be certain what you'd be deleting...