Pocket Books superceded Bantam as the published for Star Trek fiction in the early 1980s. Their line of Star Trek novels continues to this day.
First out of the gate for Pocket (if we discount the 1979 novelization of Star Trek: The Motion Picture) was The Entropy Effect by Vonda N. McIntyre, published in June 1981. My copy is from the first printing and I purchased it on 2 July 1981. I recall enjoying this one quite a bit when I first read it.
The Klingon Gambit by Robert E. Vardeman was published in October 1981. My copy is from the 3rd printing and was purchased on 12 March 1983.
The third and final Pocket Trek novel for 1981 was The Covenant of the Crown by Howard Weinstein. It was published in December 1981. My copy is from the 2nd printing and was purchased on 19 March 1983 at a store on the Sparks Street Mall in Ottawa.