Well, I did some browsing elsewhere, and I found a bunch of stuff! None of it is what I was looking for, specifically, but since I'm looking for Mega Man vocal songs in general, I thought it was quite the find.
A Moment of Passion / Asami Abe
Another Sun (I already know about this one, but I listed it to be thorough)
Asayake / All Japan Goith
Befriend / Kotono Shibuya
Binetsu / bereeve
Don't wanna be/ Spinwake
Electrical Communication
Feel the Wind
I.D.E.A ~Every Day I am Dreaming~ / RoST
It's Okay to Cry / When Dreams Come True
Lazy Mind / Showtaro Morikubo
Love Letter (I already know about this one, but I listed it to be thorough)
Monkey ~ Inside the Water
NEO VENUS
Over Shine
The Answer
I'm still fairly certain there's more, but this is what I've been able to find so far. Can anyone else help out? Any suggestions on who/where to ask for more? Thanks in advance. Mouser X over.