Some sounds I created once. They were created using festival on linux + some postprocessing.

Phrases:
"Base under attack"
"Construction complete"
"Construction lost"
"Construction sold"
"Enemy is approaching"
"Enemy is dominating"
"Enemy eliminated"
"Energy gain"
"Energy loss"
"Unit lost"
"Unit ready"
"Unit under attack"
"Unit weakened"
"Upgrade complete"

If you need more sounds either ask me (MrBeast in IRC) or try taming festival yourself.

The sounds are created with Festival, using the "slt_arctic_cg" voice from the Festvox project.
Postprocessing chain using sox:
Stretch to 110% of original length. (Slow down)
Reverb
Flanger
Normalization