To be certified to do Mac troubleshooting and hardware repair, the certification you want is the ACMT, or Apple Certified Macintosh Technician. To acquire the cert, you have to pass two exams: the Mac Service Certification Exam and the Mac OS X v10.6 Troubleshooting Exam. Each one costs $150 to take unsubsidized, and you can find excellent training books for the Troubleshooting Exam published by Peachpit (Apple does not sell training books for these exams). Pretty inexpensive in the grand scheme of things, really. And the exams are very similar in format to the CompTIA certification exams in that you have to go a Prometric tsting center and answer a bunch of multiple choice questions on a computer screen.
That said, proper training materials for the hardware exam are going to be difficult to come by in your position: the official ones cost $300+, and the only training materials I know of outside of that require you to already be working for an Apple Authorized Service Provider with access to GSX. However, I can tell you right now that aside from the service manuals, the only things on that exam that you will need that are not necessarily common sense are related to ESD safety and technician safety when working on a CRT monitor. As it turns out, those are also the two areas in which getting even one question wrong will cause you to fail the entire exam regardless of how well you do otherwise. I'm inclined to say that you'd stand a good chance at passing the exam just by going through all the service manuals and reading up about those two topics in great detail.
All this said, the grade of job this specific certification will get you is pretty much always entry level, and employers looking for people in those positions will be fine if you don't have the certification, since they can just get you on the GSX portal where you will have access to the real training materials - and I think it's more or less impossible to read through those and
not pass the exams. Just get a job as a technician with an IT company that does some Apple service, get on their GSX portal, learn what you need, take the exams on their dime, and then leave for whatever you actually want to do.
You can read up on the certification in more detail here:
http://training.apple.com/certification/acmt