The shareholder doesn't carry out purchase for ensuring the state and municipal needs, acquiring shares at other members of society. Such transaction is regulated by the Law on joint-stock companies.
Therefore, the customer who needs to buy the equity stake of society, has the right not to apply provisions of the law N 44-FL.
However the list of cases fixed in this Law when the customer can not apply provisions of the Law N 44-FL, doesn't contain such basis as purchase of shares.
Document: Letter of the Ministry of Economic Development of the Russian Federation of 18.02.2015 N D28i-397