I'm making a Magic mat for my friend's birthday, but I'm not exactly sure when it is... I don't want to ask him straight up, but I don't know if there's another way. Sheet.
If you have a rough idea of when the birthday is, ask each of your friends you know will be attending what they'll be doing for a few of those days. They should spill the beans without you ever directly asking when the birthday is.
Also, if he's having any kind of event, you can sneak the information out that way. Ask him when his birthday is. He'll probably respond with a date. Then say "sorry, I meant the time." That'll mask the intent of the question.