For grey cards you convert using things like https://kawashi.ro/eacard/
for new cards there is info here https://sega.bsnk.me/allnet/access_codes/aicc/ but the easiest way is to just read the card with your phone's NFC app (you can literally just use spicecompanion if you want)
but why would you need any of this, your physical card number is just a number, it doesn't mean anything in private servers, you can just generate a new number, especially if you don't have a reader