By doing reasonable googling. As you didn't state your topic let me make an example when [searching for conferences on magnetism][1]. The operators I use should be self-explaining. Most conferences will be announced on websites of universities or mentioned, to exclude old ones search only within `2014..2014`, and so on...

See also my [other answer][2] which has some links how to use google properly


  [1]: https://www.google.com/search?num=30&hl=en&prmdo=1&q=registration+intitle%3Aconference+magnetism+|+magnetic+material+|+physics+inurl%3Aedu+|+inurl%3Auni+-filetype%3Apdf+-filetype%3Adoc+-filetype%3Appt+-filetype%3Aps+2014..2014&oq=registration+intitle%3Aconference+magnetism+|+magnetic+material+|+physics+inurl%3Aedu+|+inurl%3Auni+-filetype%3Apdf+-filetype%3Adoc+-filetype%3Appt+-filetype%3Aps+2014..2014
  [2]: https://academia.stackexchange.com/a/455/213