HVAC parts can be purchased online at Grainger.com, HomeDepot.com and Hvacpartsoutlet.com. These retailers have parts and materials available for service and repair of all major HVAC brands. Some smaller brands may require accessing the manufacturers website for parts distributor information.
All of the vendors listed offer shipping by UPS with Grainger and Home Depot offering in store pick up, in many cases, on the same day. Should a technician be need to complete the HVAC service or repairs NATE, North American Technician Excellence, certification is suggested. Angie's List is a good resource for locating certified technicians nationwide, with a cross reference for additional licenses or certifications that may be required in specific states or municipalities.