Is there anywhere else that product designer can sell their design?  

What is anywhere else....
It is always a challenge to sell designs that are done speculatively. The reasons are obvious. The design is not made in function of a particular market or brand and it is not designed in function of the adequate technology for the quantities that a particular brand or organisation can sell. So...unless you have researched those elements carefully, you are on a fishing trip. As we say in the low-lands: you never know how a cow catches a hare...but it is as unlikely as that.
My best advise is always not to look for a manufacturer or more popular these days: an editor, but to climb the mountain from the base. Take your renderings, prototype, mock-up, model, 3D modelling whatever to the kind of store where you as a consumer would expect this product of yours be sold. The advantage is first of all that you get the advise of someone that is close to the consumer. If the store sees the potential, ask them where they would like to buy it. Most of the time they will mention a wholesaler, not a manufacturer, but in both cases you contact these people. You give yourself one advantage, you can start your inquiry by saying: "This or that retailer (obviously a good client of them) recommended me talking to you about this new product I have designed. A manufacturer or wholesaler will not ignore the recommendations of one of there clients. From distributor you go to importer or directly to manufacturer, depending on the recommendations you received.

Tangent: how do you turn off intellitext in body of a DA post?
I'm experiencing a creeping blight of intellitext (highlighted, or underlined text in the body of a post). One showed up in Koen's post above. If I click on it, it brings up an advertisement. How do I turn off intellitext ads? I surfed about intellitext to learn how to turn it off, but did not find a useful technique. I did learn that intellitext was developed and flourished briefly 5-8 years back and then it receded in use. Now the advertizing and PR predators are adapting it to guerrilla advertizing and it is spreading like a cancer spreading after a remission.

My Internet
connection, AT&T Yahoo!, has begun using this device -- supposedly as a benefit. I just ignore it. I can't imagine why it would show up in your DA text. . .