Attending construction trade shows is a good starting point. You will find some good leads and order something from them first. As you stay in the industry for some time, you will find more good vendors (employees at your current vendor might tell you some info, or people in related industries might also give you lots of insights. For example, construction tool suppliers know all major construction material suppliers).
Internet search did not help me much. Everyone can put up a fancy site on Alibaba, but you have to physically go to the factories to see their quality and manufacturing capacity.
You can also ask friends in this field. Friends not in this field will not be very helpful.