How can I get the precious metals out of a catylitic converter? How much is in a large or small one?

Do I need any permits to do tis regularly from my commercial garage space?

There is an extremely small amount of these materials in even a very "dirty" catalytic converter. You would be looking at parts per billion measurements of the concentration of anything outside of the typical carbon, lead, sulfur and various volatile organic compounds that accumulate in the converter. You would generate a massive amount of hazardous materials in the process of removing enough accumulation to result in a measurable amount of anything valuable --- just from the deposits themselves, not including the array of chemicals that would be required to extract them from the converter. To get one gram of platinum, you would need something like 100,000,000 grams (about 110 US tons) of catalytic converter deposits.

If you are considering processing hundreds of tons of combustion products and heavy metals mixed together, I am certain that you would need a lvery arge number of permits to even think about doing it. You would probably be well-advised to obtain, in addition to the permits, some serious psychiatric treatment.

It takes a lot of specialized equipment to get this stuff out and the metals aren't worth your time. Send these into a recycling facility to do your part for the environment.