Can a microbusiness obtain marijuana from a marijuana grower or processor?

No.

Section 10(1)(f) of the Michigan Regulation and Taxation of Marihuana Act (MRTMA) MCL 333.27960(1)(f) states, in part, that lawful activities for a marihuana microbusiness or an agent acting on behalf of a marihuana microbusiness who is 21 years of age or older include, cultivating not more than 150 marihuana plants; possessing, processing, packaging, storing, or testing marihuana from marihuana plants cultivated on the premises; selling or otherwise transferring marihuana cultivated or processed on the premises to a person 21 years of age or older; or receiving compensation for goods or services.

This section of the MRTMA specifically states the marijuana possessed, processed, packaged, stored, tested, sold, or transferred by a microbusiness must be from plants cultivated on the premises. Therefore, the MRTMA specifically prohibits a microbusiness from obtaining marijuana from any source other than plants cultivated or processed by the microbusiness.