Remember that anything you reveal to an attorney -- even a tax attorney -- is utterly confidential and can't be revealed to anyone else without your permission. That being the case, be as straight with them as possible, and don't keep anything hidden; you never know what might help your case.
Most American states (and many foreign countries) have Tax Lawyer Associations of one kind or another. Check to see if your prospective tax attorney belongs to one; this will signal their commitment to that particular specialty. Tax Lawyer Associations may also be able to help you find a tax attorney if you can't find one on your own.