Keep trying on SOLAR. I got all 3 of the electives I wanted by doing that. Remember SOLAR opens again in July and that's a great chance to get what you want.
Emailing the profs may work but unless its a degree requirement they're not obliged to give you a spot. If you are emailing them, make sure you mention something like "I want to minor in _____" or "I'm looking at a future in _________".
Good luck and hope you get all your electives like I did!