I haven't heard of an spanking gatherings, I guess the closest thing that you are looking for is a munch. It is specifically for people with interest in bdsm, and spanking would definitly be a fetish for many attending. I've heard of many in Toronto, but haven't gone to any just yet.

If you are a sub, perhaps it may be good to attend one (go with a friend preferably) and hopefully learn a few things.