Can I get continuous power from a light controlled by a switch?
Yes, but probably not in a terribly convenient manner as you seem to be hoping for. 

You'll need to find where the power is supplied to the lighting circuit:


It may be power to the switch and then switched power to the lights -
in which case you'll need to run a non-switched wire from the power
source at the switch to the place you want the new light.
It may be power supplied to one of the light boxes, and then a "switch loop" down to the switch - in which case you can tap continuous power at the light fixture where power is supplied on the feed side of the "switch loop." If that does not happen to the fixture you'd like to connect to, you'll need to run a non-switched wire from the power supply to the place you'd like the new light. If it does, congratulations, you've won the terribly convenient lottery.
it may be simpler to connect to a non-switched outlet circuit, if there are outlets in this garage as well as lights. If you're looking for one on the ceiling level, look at the garage door opener (or where one would be if there was one.) If none are convenient, again, run wire.