Signage contractors are used to doing things their way, which means nothing has changed in 20 years. I still see T12 specified for all back lighting in signs.
Fluorescent and LED is available in either 120V or 277V. But not from every manufacturer.
1. Try to work with this signage contractor to get the ballast and driver for their signs at 277V.
2. Find another signage contractor who will work with you and find something that will work at 277V.
3. Take the lighting out of the signage contractors scope and pick out your own lighting that will work and is available at 277V.
4. Or finally, manage to work something out to provide the 120V power as requested.
Here's an example of an exterior LED spot light at either 120V or 277V.
http://www.acuitybrandslighting.com...Sheets/Accent/Accent Lighting/4640_KM_LED.pdf