I'd first like to mention that the Font Awesome widget library in this forum thread is for version 4.7 of Font Awesome. If you're using version 5.0.10, the icons from this widget library may not work with the Font Awesome 5.0.10 font.
With that in mind, please download the Font Awesome 5 ZIP file from here:
Unzip the ZIP and go inside the "use-on-desktop" folder. Once inside, double-click to install the "Font Awesome 5 Brands-Regular-400.otf", "Font Awesome 5 Free-Regular-400.otf", and the "Font Awesome 5 Free-Solid-900.otf" font files. At this point, please ensure that these fonts have been properly installed on your machine by opening up your Font Book (for Mac), your Font list (for Windows), or your FontExplorer app. If you had Axure RP running during this time, please exit it so that it updates with the installed fonts.
Once that's done, you'll want to copy the icons from the site below (since there isn't yet a Font Awesome widget library built for v5.0.10):
Here's a screenshot to demonstrate where you can copy the glyphs:
And then paste the icons into Axure RP. If the icons are rendering blank or with a question mark, make sure the proper font is selected. For the "accessible-icon", for example, it looks like the selected font for this icon should be "Font Awesome 5 Brands".