I figure that soil microbes and plant roots have millennia of practice. If the conditions in the pot are good, dust from air and water are likely to bring in something close enough. The roots will encourage the ones they like best.
If indeed a pot CAN maintain a healthy enough environment to sustain as many kinds of microbes as are needed to have a healthy "population", they probably don't NEED us to supply fancy powders and liquids that are mostly sold to home gardeners, not savvy professionals.
Some microbiologist, perhaps many years ago, put out the theory that "Everything is everywhere". When you include spores, airborne dust, ground water and animals, you can almost rely on any plant in the ground encountering enough microbes or spores of microbes that it can eventually find any species it needs, and encourage that one to multiply.
Since the commercial products each only provide a few species of MR and other microbes, why not take a teaspoon of soil from each of your healthiest beds and pots and mix them, and keep them aerobic, and well-provided with OM. Maybe make tea from the soil samples.
Then sprinkle a 1/4 tsp of soil inoculum onto each pot you want to inoculate and water it in.
It can't hurt unless you import some plant diseases.
Many people swear by "compost tea" or "manure tea" to provide "beneficial" microbes.
