The transmittal and new exhibit templates can be found on the CMS website. There are also downloadable Moss Adams templates.
For more information related to Transmittal 18 and bad debt reporting requirements, you can view these resources:
What Hospitals Need to Know About CMS Transmittal 18
CMS Transmittal 18: Medicare DSH, Worksheet S-10, and Bad Debt Reporting
Centers for Medicare & Medicaid Services (CMS) Transmittal 18 FAQ