TRICARE Dependent Coverage Extension Act - Deems the following individuals as dependents, for purposes of dependent coverage under TRICARE (a Department of Defense [DOD] managed health care program): (1) a child who has not yet attained age 26 and is not eligible to enroll in any employer-sponsored plan; or (2) a person who is in the legal custody of the covered member, has not attained age 26, is not eligible to enroll in any employer-sponsored plan, resides with the member, is not otherwise a dependent under TRICARE, and is not the child of another covered beneficiary. Requires a premium payment for such coverage.