Can you share more details? This is a world I know nothing about.
There are many which are less modernly advertised (usually paper/newsgroup/email) that will draw 100+ people easily.
Including planned events with participants in the dozens, Id say you could count at least 100 a year. I'd consider that since that's the population of smaller tech conferences.
Not to rain on anyone's parade, but that event is about hammers just as much as embedded programming is about C.