Some people need a new I-94 because they lost their original and need a replacement I-94; others need it because paper I-94s are no longer being issued. I will cover both processes below.
How do I get the paper I-94 if I didn't get one at the airport?
There has been a recent change in how I-94s are issued. If you have traveled since April 2013 you may have noticed that paper I-94s are no longer being issued at the airports. If you need an I-94 in order to receive a social security card, state ID or drivers license etc then you may want to visit this website to print the I-94 and bring with you.
Do I need to print out the I-94 if I am filing for my green card based on marriage to a US citizen?
No, if you are just filing the adjustment of status forms (I-485 or even the combo I-130 and I-485 forms together) the CBP website states that you can simply use you visa stamp that has all of your information along with your biographical passport page as proof of valid entry. You should also bring that passport with you to the interview. This information also applies to any other immediate relative green card applications filed in the US (ex parent filing for child under 21 or a child 21+ filing for parents).
How do I get a replacement I-94?
If you had a paper I-94 and lost it or lost both the I-94 and your passport containing and you need a replacement for valid proof of entry to the US, then you will need to file form I-102. That form needs to be filled in with as many specifics as you can remember about when you entered the country. You can file the I-102 with your adjustment application forms (green card application forms) and it should be decided in around the same time as it would take the other forms to be scheduled for an interview. You can also file it as a stand alone form.
I hope this information is helpful. Do not hesitate to contact me if you or anyone you know needs assistance.