My school does offer instructor training...
However, many would-be instructors have something in mind that requires a shorter-term commitment.
Herein lies the problem.
Are the prospective instructors already skilled at tai chi?
If they cannot do it themselves, how do they expect to teach it?
To teach, you must have experience.
And experience takes time.
To perform tai chi skilfully requires decades of training and ongoing corrections and development.
It is not akin to keep fit or yoga.
At its heart it is a Chinese martial art, and even if your intention is 'health', a thorough grounding in the principles of the art are necessary.
Popular culture gives the impression that people can qualify to be a tai chi instructor in 2 years or so.
This is ridiculous. And unethical.
How long does it take to learn how to play the piano, to dance, to pass a degree?
A person may learn how to drive a car in a matter of months, but are they then a driving instructor also?
To teach, you must possess the skills.
Possessing the skills demands time and daily practice.
Attempting a shortcut is unethical, ill advised and dangerous.
Who will insure you?
If someone is injured because of poor quality tuition, you may be liable for malpractice.