Sergio, if you bought it new, and if it was certifiable, all that certificate will tell you is that it was made to the manufacturing tolerances and specifications in effect at the time it was made (called the "short form"). It will contain traceability info to the NIST though. If you have to have it certified for an SPC or quality program like ISO or QS, that certification does not mean anything. There are shops in most major cities and manufacturing centers that calibrate tools. These can check your wrench, repair if necessary, and test to confirm that it is in tolerance. They will then issue a certificate with the actual values and deviations (the "long form"). This will also be NIST traceable. I'm not as knowledgeable on torque wrenches as on precision measuring equipment. Some shops that do measuring equipment do not do torque wrenches but I'll bet that they know someone that does.
You might call the American Association for Laboratory Accreditation (A2LA) in Frederick, MD at 301-644-3248 if you come up dry on a local source. Your can also check the Sears site if all you need is the short form. Sears sponsors this one but it is not their "official" site. Bet you will not get as much info from them as you got here though.