The only thing I can say is to request it from the publisher. I have made a promise to the publishers and to the textbook authors to not distribute the key. In fact, it's deleted and I do not have a copy.
We use to have a key on Texttkit that was created by a forum member. It was his independent work and his view on the answers where he wished to share and help other learners. However, I took it down. He posted the key at Textkit for the benefit of adults and independent learners. However, I was contacted by Mr. LaFleur himself who made a very compelling argument that in this day and age, having keys online to popular textbooks which are used at highs school and college level classrooms causes more harm than good. While my natural view on things is rather libertarian where I side with the individual, in this case a greater-good argument won me over.
For me, Mr. LaFleur gave me a new perspective on what's happening in classrooms these days. He shared with my that the key directly resulted in students receiving failing grades and in even expulsion when they are caught. Textkit is about helping each other learn and in this case it was causing the opposite. There are times when we are forced to rethink our good intentions and this was one case where it seemed to me that a key was off-course from our intentions.
The whole subject of the roll the Internet plays in academic dishonesty is a subject I am far removed from. I'm not an educator. I'm both older (the Internet was just getting going in any meaningful way by time I completed graduate school) and I didn't understand how the Internet has caused a wildfire of academic dishonesty. I'm saying this just for some background on how we have arrived at this point and I wish you luck learning Latin.