Any mechanical engineer can design a carabineers. If this is going to hold up personnel it will have to be designed to the EN specs that covers carabineers to prevent any accidents and covering you know what. You will. have to have some type of testing done with the prototypes. Watch out for patents.
Having said that, I know you can go into to places like Harbor Freight and there are usually several sizes with no indication of codes or standards I just bought some.
I would go straight to the climbing gear manufactures - petzel, black diamond etc. Black Diamond have done some work with Kayak manufacturers on building custom bits with them, so they may be open to collaboration. Of course this won't work if you are competing with them. Getting their name on it may be worth something to you if you need confirmation of quality.
A machined version may work, but will be a lower strength than a similar forged version due to grain differences and work hardening etc. It will be significantly cheaper though for small quantities.
I would pick my machine shop wisely for this. Someone doing crane hooks etc will be your best bet to understand material choice, stress concentrations etc.
You are in the general public looking for an engineer to sell his services. In the U.S., that means you need a registered PE. At a minimum, that means he is insured so that your survivors can sue after your carabiner fails.
Not sure of your exact application or whether this will be a marketable product or a 'one off' production, but any general engineering group could take care of this for you.
They will ask about application, loads, quantity, form/fit/function, material preference, desired costs of production, etc.
They will charge you a number that will seem to be way too much if you are just making one. But if you are lifting or doing any life safety with this device, their expertise will be worth every penny.
In looking for that engineering group, you would like them to be licensed (this may actually be required) and you would like them to be experienced in this area (product design, lifting, rigging, fall arrest, etc.).
What zcp says. Be very careful with this kind of kit, death injury and equipment failure are likely with badly made kit or poorly understood load conditions.