Lenski's old books are hard to find. I gave one to WELS VP Huebner and inscribed it in the hope he would abandon Church Growth dogma. He did not thank me, even though he asked me for one when I found it.
The Eisenach Epistle book is over 1000 pages. It is linked below. Alec Satin prepared the PDF. He exhales classic books!
Lenski Eisenach Epistles Dropbox Link