How to perform AMT calculations on ISO options without knowing the FMV on day of exercise? (see details)

I was awarded 50k ISO stock options on 2014/6 which vested after 4 years 2018/05. The strike price of each stock was $0.50 each. I exercised options on 2018/06 by paying ($0.50 X 50k = $25k) when I left company 'X'. 'X' has not gone public yet. 

Q1) What forms are necessary for me to report AMT on this? How do I obtain these forms?

Q2) Is company X required by law to furnish Form 3921? 

Q3) What other info do I need from 'X'? I cannot seem to understand how to obtain FMV on the exercise date?