Knives that are produced by more than One person do not fit the usually definition of 'custom' knife. You can arrange to have many knifemakers produce a knife to your specifications. But if you want to have someone agree to manufacture knives of your design and to pay you a royalty on each knife, your pretty much SOL unless you happen to be a very well known knifemaker. Even then, they come to You, not the other way around.
If on the other hand you have a significant supply of money, and want someone to produce thousands of knives of your design, which you will then attempt to sell on your own, I hear there are a lot of places overseas that would be glad to help you out for the right price.
I seriously doubt that any 'custom' knifemaker will be able to help you. Most are lucky to produce hundreds of knives in their lifetimes, let alone thousands. Nor would they want to.
Les is right, real custom knives Are made by the thousands. But they are all just a little bit different. And none of them were made by a factory. Some knives are produced according to a custom makers design in collaboration with a factory, like the Spyderco Centofantes, or the Benchmade Pardues, or the Kershaw Ken Onions. But nobody would call these Real Custom Knives.
Paracelsus, curious about just what the Titanium Anglophobe thinks is a Custom knife