Guilds usually keep lists of LA quilters, and if they have a newsletter you might be able to buy an ad. Join all the guilds in your area, and attend their meetings. Quilters are often more likely to give business to someone they know. Enter your quilts in shows to get more visibility. The Ultimate Guide to Longarm Machine Quilting by Linda V. Taylor has a lot of information for longarming as a business, including various ways to advertise. Good luck with your business.