Where to find insurance agents that deal with construction bonds in the US ?

Your best bet is to go to any of the yellow pages and search advertising, says construction insurance, call your current agent and ask a local reference (probably not going to, lol), or by placing your zip code in the www.iiaba.net agent locator button.

Travelers do a lot of construction, you could even call and ask for an agent in your area that does a lot of construction insurance.