What manufacturing companies advertise?

Find who buys whatever the manufacturers you're interested in sells. Then figure out what they read, what is their national association, what publications does it have.

For instance, if you were Caterpillar and wanted to sell some buldozer, you'd want your ad to be in front of people who buy for large construction and road repair companies and such.

You might consider placing an ad in Contractor Magazine | Home (There are ads on the site, if you click on tabs, for various products that general contractors, big and small, but not too small, it seems, might find useful.

Hydronics | Contractor Magazine has several ads for Utica Boliers. They take you to Utica Boiler's website. On which, there's a tab called Tradeshows. Click on it and you find out the next trade show Utica's attending. It's going to be in January, in Chicago, and they're booth number is 2810.

Which means you could advertise to them at the trade show too.

If you are interested in manufacturers of fasteners, nails and bolts, you'd have to figure who uses such things on a large scale. Home Depot might be a buyer you're after. So, how do you advertise so that Home Depot procurement department people see your ad?

I'm betting someone publishes something called "Large Warehouse Store Procurement Manager" or something like that.