Polygamists have been excommunicated since the church ended the practice in 1891, or thereabouts.
Those practicing polygamy when it was sanctions by the church were not excommunicated. Why would they be?
Sanctioned by the church eh? You need to re-read the BOM. Jacob 2:23-24 - "But the word of God burdens me because of your grosser crimes. For behold, thus saith the Lord: This people begin to wax in iniquity; they understand not the scriptures, for they seek to excuse themselves in committing whoredoms, because of the things which were written concerning David, and Solomon his son. Behold, David and Solomon truly had many wives and concubines, which thing was abominable before me, saith the Lord."
The first edition of the Doctrine and Covenants, printed in 1835, also denounced the practice: "Inasmuch as this church of Christ has been reproached with the crime of fornication, and polygamy: we declare that we believe, that one man should have one wife, and one woman, but one husband, except in the case of death, when either is at liberty to marry again." (Doctrine and Covenants, section 101, verse 4) This denial of polygamy, was printed in every edition of the Doctrine and Covenants until the year 1876. At that time the Mormon leaders inserted section 132, which permits a plurality of wives. When a 'prophet' is caught in an adulterous affair how convenient, he suddenly gets a new 'revelation' allowing polygamy. Nice.
Now you want to provide ONE Scriptural passage from the Bible where God Himself COMMANDED polygamy?????? Specific Chapter and verse. Then when you've done that please provide SPECIFIC Chapter and verse where God ever told Abraham, or Jacob, or Moses, or whomever that polygamy was REQUIRED for salvation as Brigham Young preached in 1866: "The only men who become Gods, even the Sons of God, are those who enter into polygamy" (Journal of Discourses, vol. 11, p. 269).