I just released
Secure Shell (dev) 0.8.24.2, which adds the 'user-css' preference.
This preference can be used to add a custom css file to the terminal window. It's intended as a roundabout way of using web fonts, but you might also find another creative and borderline-unsupported use for it.
The monospace fallback is there because the new-connection dialog and preference pane don't respect the user-css pref, so they won't know about "Source Code Pro".
You can find other Google web fonts here: http://www.google.com/fonts/. Keep in mind that you must use a monospace font (all characters must be the same width), or you'll end up with all sorts of alignment issues. There doesn't seem to be a way to search the Google fonts for monospace, but I stumbled across Inconsolata, Source Code Pro, and Oxygen Mono while scrolling through the options. Set your sample text to something like "xX.1#" to make them easier to spot. There are probably more.
Rob.