Golf demo days are events put on by the golf club companies themselves, or by the hosting course or practice facility. Sometimes the event is dedicated to the equipment of just one company, other times multiple manufacturers are represented.
Company representatives are often on-site to answer questions about equipment, and staff members from the host facility are usually willing to provide quick swing checks and tips.
You can try different shafts, different lofts, different clubs. And best of all, demo days are (almost always) free.
Golf demo days are usually promoted well in advance by the host facility. If there is a golf association in your city, that association may well have a list available of such coming events.