Hi John. Generally, libraries that pay for tracks expect a high level of production value. They are also prized clients of composers that may make a good chunk of their living from such gigs. For that reason, it’s unlikely that you’ll find people willing to divulge such info on a public forum. That said, to start things off, you might want to check out the big libraries, who do pay nice upfront fees: Killer Tracks, Warner Chappell, Megatrax for example. Just make sure your demos match or exceed the quality of what you hear on their websites.