Acceptance rate of an IEEE conference
If googling "acceptance rate " does not yield a response, it's a good bet that the data is not online. If you are desperate about this information, you can still try to reach out to previously accepted authors, as sometimes the acceptance rate is communicated as part of the acceptance / rejection letter.

That being said, I really wonder why this info would be so essential to you that you go through great lengths to unearth it.