Try the equipment supply online catalogs. They have photos of their equipment without watermarks.
To wit:https://epicsports.cachefly.net/images/73669/300/football-premium-down-box-and-chain-set.jpg
Just because an image/graphic doesn't have a watermark it doesn't mean it isn't without copyright protection.
All images/graphics are copyright protected as soon as they are taken/created and with rare exceptions, they stay under that protection for many years after the death of the photographer/creator.
Now having said that, you may find the manufacturers have acquired (bought) the copyright from the creator and they may be happy for the use. That however can't be assumed.
What is it exactly you want a picture/graphic of and for what use? As a photographer myself I've recently shot three NFL games at Wembley and as some of my colleagues were doing the chain crew I have plenty of photographs that may include what you need. Depending on what you want them for I would likely be happy for you to use them for free.
