Hi Mags, I love it that you are using sources often enough to want a drop down list. Like you, I was borrowing with copy and paste to move sources into the next profile. I then made a free page where I could keep all my sources. That has been helpful but not to the extent I hoped.
I'm going to switch from viewing my source list in another tab of the same window, to opening a new window that can share the screen with the profile I'm working on, because the back-and-forth can get annoying.
Mary's idea of a word file would also work well for me, but I'm afraid we are light years away from a drop down list of sources, although I love the idea.