Most people have a copy of their green card, and they submit a copy of the GC with the I-90. That's how you would find that information when the card is lost.
If you work, your employer probably has a copy of your green card, which they made for the I-9 paperwork. Go to HR and try to get a copy of the copy or at least look at it and write down the information.
If that's not possible, look at the I-485 approval notice. It will have the date. Sometimes this is a few days later or earlier than the date on the card, but it's still close enough that it won't cause a problem with renewing the card.
Somewhere in the top right of the I-485 approval notice you will see a line that says "COA: ___". That would be your class of admission. Based on how you got your GC, I can deduce that your class of admission would be CF1.