I can't have the IDs of those who chose a user name, if i told you do this:
Open the page that shows all your fans, and harvest the links (open in new tab "people like this").
Scroll down and let the whole list load (depends on how many fans you got), and then harvest them links.
Each link will be very basic: starting with "/profile.php?id=" and ending with "&ref=pb".
Open a notepad, replace the quoted with a blank space - and there you go, a list of all your IDs.
I hope it helps.