Generally, the best way to locate information on acceptance rates is to visit the journal website and check the author guidelines section.
Another option is to contact the journal editor directly. If the editor won't supply the acceptance rate, ask how many submissions the journal receives a year. Calculate the rejection rate by dividing the number of articles published in that year by the number received. For example, a journal that receives fifty submissions annually and publishes only ten, has a rejection rate of 80 percent (returning 4 out of every 5 submissions), or an acceptance rate of 20%.
Additional resources for locating acceptance rates: