You will struggle to get a list of the types of companies as they are used practically everywhere. Anyone who has a warehouse is a good bet. There are over 80 accidents on the website and studying these may help you.
2 ideas. Search on OSHA database of forklift accidents. They’ll show it split by SIC codes, once you have SIC codes you can search that way
Another way would be to look at UCC filings. UCC filings are public on leased equipment. Pull up UCC filings in major cities like Chicago, LA, Atlanta. You’ll get a big list of large forklift users.