First, the Princess Auto equivalent in the USA is Harbor Freight. Lowes is more like Home Depot or Rona.
Second, we have a Bolts Plus where I live. They usually carry every shape and size of bolt, nut, screw and fastener I've ever needed. Also, our local Fastenal store usually has all kinds of fasteners as well but I find them pricier. Another name we can access is Debrasco or something like that. I obvious don't shop there but I have driven by it.
Since you know the bolt you want, perhaps asking the aliens (Google it) will help? It's likely going to be an industrial/commercial hardware supplier that will carry what you want. Good Luck Mike.