The easiest way I can think of is to find a good quality WAV file of the sound, open it in Audacity, open your project in a separate Audacity and just copy and paste the first in wherever you need it in your project (once you’ve hit copy on the first, it will remain in your copy “memory” until you do another copy so you won’t have to keep switching back to it).
Of course, you could also record the sound yourself but finding one may be easier and faster. There seem to be a lot available:
I would suggest creating a separate track for the page turn sounds, that way it will be much easier to adjust the timing relative to the recording of your voice, and less chance that you will accidentally paste on top of your speaking.
This should not happen if you only set the cursor and do not select part of the audio.
If you want to do it with two tracks, sync lock has to be enabled in order to force gaps while inserting the page turn sound into the second track.
You can also define a (region) label just after pasting the sound into the first track, the shortcut is Ctrl-b.
If one sound is wrongly set, you can delete just that label (+ audio) and make a new attempt.
I was able to use the copy/paste–super easy! Since there are a whole lot of page turns (it’s a book for a very young child) I left some “silence” between pages of reading so it was easy to paste in those spots.