It seems there a growing number of bands in this category that have had some success-Explosions in the sky, Moreau, El Ten Eleven.
I’m not much of a singer, but I can write and arrange music quite well.
How much harder is it to pitch music like this?
If the latter, absolutely! Get soundtrack work. Place your music in TV, movies, games, and commercials. Lots of work available for instrumentals if you're not trying to be a rock star
This is something I've wondered about for a while. Where would be a good place to start if you wanted to pursue something like this? Are the any websites, forums or organisations that would be worth a search?
That I'm afraid I won't be much help with. One of my bands used a company called Tinderbox to get our music placed in a bunch of catalogs for general use in TV. And that's as much placement as I've ever done. It cost us $3k and got us about 30 seconds of time as background music on a couple MTV reality shows.