Hit a curb and ended up with a sidewall crack big enough to stick a finger through. Is it repairable?

No. Damage to a tire's sidewall is not repairable. I can't think of any shop that would try to repair one, and if they will, then they're not a shop I would trust.

Is there even a way to repair that even if someone was willing to! Had that happen to me once on my e36, I hit (more like hopped) a curb on a sharp right hander and all seemed ok, until the next day when I found the tire completely flat and then noticed the sliced sidewall (it took a while to deflate completely). Got a new tire right away.

It depends on where it got damaged and how bad it was. Typically it isn't repairable, but it also doesn't mean you can't drive on it. Like I said, it really just depends.

Post up a picture.

-Don

99% of the time you'll need a new tire.

I don't even see how 1% of the time you could get by without a new tire. If you have a crack large enough you stick a finger through, you'll need a new tire 100% of the time.