What is our best bet for finding safe, nontoxic building materials for our new home’s construction?
First of all, make sure you are working with a builder or architect who is a legitimate green professional. Check with a local chapter of the U.S. Green Building Council for a referral to a LEED AP (Accredited Professional) or ask a local Home Builders' Association to find a CGP (Certified Green Professional).
There are also numerous resources available to help with the vetting of building materials for green construction. The book Green Building Products: The GreenSpec Guide to Residential Building Materials is now in its third edition. This book will get you started, although you may have to dig a little deeper with material safety data sheets (MSDS) and other specification information to find out exactly what you want to know.
A web resource that comes to mind is BuildingGreen.com, where you'll find green product listings and other useful information. (A subscription is required to view some parts of the site.) Greenguard is another trusted organization that certifies building materials for a minimal impact on indoor air quality.
I am hesitant to recommend retailers because of the potential for greenwashing. (Greenwashing is the attribution of "green" qualities to a product that is minimally sustainable at best.) It is best to first research products that have been third-party certified and then find a local distributor or retailer. However, some stores in your home state, like Bluegrass Green Co., seem to be on the right track.
I also recommend trying to find local sources of materials within 500 miles of your project site. These materials will have less total embodied energy wrapped up in transportation to your site. The local Home Builders' Association might be another helpful resource for site-specific issues.
Finally, you should be able to find an FSC (Forest Stewardship Council) lumber supplier in your region. FSC is a third-party chain of custody system to ensure that any lumber and plywood products you purchase are from sustainably managed forests. Graf Brothers is one supplier of FSC-certified lumber in Kentucky. The FSC website also has a database of manufacturers and distributors of FSC-certified products. When buying your lumber at a lumberyard, it is important to check each piece for the FSC tag, as some suppliers may mix inventories from managed and non-managed forests.