Yes it's possible but you will have to get lucky with buying an SE that hasn't been sold in a while. IOS 9.3.4 is unjailbreakable was released on August 4, 2016.. So you need to find an Iphone SE manufactured in July or earlier. I believe if you were to buy one now, it would already come with 9.3.4 or higher. because all units manufactured after mid August are going to have that update pre-installed. So you would need one that has been sitting in the back and hasn't been sold since mid August.
Your options
1) Buy an iphone SE and hope that it was manufactured before mid August.
2. Buy it off someone and verify IOS version is 9.3.3 or earlier.