What part of CL are you advertising on?
Get some cards made, hand them out to people. When I do a pickup, I hand a few cards and ask them to call me if they have anything in the future, or to pass it on to friends/family.
Make up some flyers with tearoffs and post them around town.
Drive around early on trash day and glean stuff that way.
Knock on doors of homes that you see scrap laying around. Ask what they plan to do with it and if they'd like you to haul it away.
If your local newspaper is online, see if they have a free classified section you can post to. Or even post a paid ad if you wish. I prefer not to pay for ads.
In addition to CL I post to several other sites, including kijiji.com which is an eBay
Think of everything you do as a fishing pole. Some will get bites, some won't. Just keep at it.
I am thinking about getting magnets made for my van. Advertise 24/7. Get the eyeballs of people that don't even own a computer. Yes, there are a few out there.
Maybe even a small sign in your yard "I pick up scrap metals". Or "free scrap removal".
Good luck and it will come, just keep on keeping on.
Above all, be professional in your dealings.