gatorguy415,
Welcome to the board.
The experience you relayed in your post really doesn't surprise me. In fact, I'm saddened to say, it's typical. IMHO, we, as an organization, do a SORRY job of re-capturing the talents of thousands of Eagles, just like you, who are, as in your case, at a point in their lives where they can afford a little time to honor the Eagle charge and give something back to the Scouting community. If you've been out of the loop for a while, things have changed (dramatically, and [mostly] for the better, I might add)... Two-deep leadership, Buddy System, Background Checks, required training, etc, etc, etc.
MBCs must be certified by the District or Council Advancement Committee. There are two ways you can go about this...
One, you register as an Adult Leader with a specific Unit (Troop, Crew, or even a Pack for that matter). I strongly suggest you check out two or three Troops close to home. Just look them up, drop in on a meeting (and observe), introduce yourself to the adults; but you want to get to know the Troop's Committee Chairman (CC)... state your credentials; state your intentions. Once you find one you like, ask to file an appl. and fee (about 10 bucks) with the CC to be on the Troop Committee. You'll be expected (or you should be) to complete, within one year, Basic Training (New Leader Essentials) and Troop Committee Challenge. You'll also be required to take Youth Protection training, which must be re-certified every two years. MBC training is a snap; but, it's very important. As a registered Committee Member, you'll be expected to participate with the Troop by sitting in on an occasional BOR. You may be expected to purchase and maintain a uniform. Once you've completed Youth Protection and MBC orientation, you can choose one or more MBs that you would like to teach, file an MBC application (local form). The Troop's CC or Advancement Chair can help you with that. Going this route gets you officially back involved in Scouting while imposing the minimum impact on your time.
The second route, is to get with your local District Advancement Chairman, and tell him/her what you want to do. You file the same application and are subject to the same background check; but, there's no fee, and no uniform is necessary. However, you'll still need to complete Youth Protection and MBC training. And, you'll need to file an MBC appl. (again, local form). Unfortunately, going this route, you don't really get tho know the local Scouters. But, I guess, if you're a Dentist and want to teach Dentistry, or are an Attorney and want to teach Law, this route might work well... especially if you were to visit a local Roundtable meeting once or twice a year, to get acquainted with the local volunteers.
In either case, the bottom line is getting to know the volunteers who are involved in Scouting at the local level. This may seem counter-productive, but it's a method with significant checks and balances that's in everybody's best interests, including yours.
I suggest you contact Rich Watkins (WatkinsRC@gru.com), who is your District's Advancement Chairman, tell him about you prior attempt, tell him about our conversation, and ask him for his guidance (and for the names and telephone numbers of the CCs of the three Troops closet to your home).Let me know how it goes for you.
Disclaimer: I have no experience as a District Advancement Chair, so... I may not be completely on target; but, my guidance is based on my experience which was similar to yours.