Accountants, tax professionals and bookkeeping/ payroll services all belong to a "stick with who you are most comfortable" service provider business. You're generally going to stick with your accountant and payroll service (if you're using one) unless something major upsets your relationship, or if you find something substantially better than how you're presently working.
Your Problem: how do you attract new clients to your service, and still come out ahead after your marketing expenses? Let's assume most small businesses spend about what I spend each year with my accountant --$2,000 (they save me much more than that each year, so don't start calling to get me to switch).
One solution: You need to select a good list of prospects and keep in touch with them on a regular basis. You could develop a newsletter and mail it out every month (quarterly is not frequent enough to build up a strong rapport). For a thousand prospects, expect to spend about $1,000 a month in printing, writing, editing, mailing and postage expenses (more if you consider your lost opportunities for the non-billable hours spent doing all this yourself).
Better idea: Use the same list of prospects from the first approach, but mail a simple postcard once a month reminding those prospects that payroll taxes are due by the 15th of the month. Send the card out first class on or about the 8th of the month so it reaches them in time. All it has to say is "Don't forget -- payroll taxes are due by the 15th," or whatever schedule your state works with (you'll have to account for all the new deposit rules imposed by the IRS, but it's important to remind them of something on a regular basis). And remember to mention your company's name -- "This reminder comes to you from ABC Accounting Service. If you have any questions, call Joe Accountant at 555-1212."
Cost per mailing, including the card and postage, is about $250 per thousand, or a quarter apiece. At 12 times a year, that's only $3 per year per prospect! You'll be remembered the next time your prospect misses a deposit date. And there's a good chance you'll pick up referrals from your prospects -- when the people you're mailing to (your prospects) hear about their associates missing occasional payments, they'll mention your name as the accounting or bookkeeping service that goes the extra mile to keep you on your toes.
Recommendation: include your present clients in the postcard mailing. You want to keep their business, too. As a safeguard in case the mail is delayed, you may wish to include all the scheduled deposit and due dates for the next month or two.