Hey STM,
I'm launching my own supplement offer and I'm looking for a doctor to be the spokesperson.
Like this: http://3harmfulfoods.com/video_170428.php?cad=1
Where can I find someone online (Besides upwork) before searching local?
All I basically need is their endorsement and right to use their name/credentials/story in the copy.
To be honest, ... unless you are willing to really REALLY pay a lot to that person ... I am not sure too many real medical doctors in the US will be willing to risk their medical license and the $500,000 + 8 years they have spent in university + medical school to be a spokesman for a product that has not passed FDA approval.
Maybe in doctors in countries where salaries are very low may be willing, but I would be doubtful in places like US, Western Europe or Nordics.
I'm pretty sure most of these "doctors" used in videos like these are just paid actors, which should be listed in the TOS somewhere. I've seen numerous examples of this, the doctors were not even real doctor in the first place 
The example you used seems quite legit thought, this Amy Lee doctor really seems to be a doctor and looks like she's part of the company producing the line of products sold on the nucific.com website. Since she's directly involved, she most likely knows the products in and out, that's why she's putting her name on it.
But as cmdeal already mentioned, it would be very hard to find some real doctor to put his career at stakes just like that, by backing an untested product with his name.
If you just need a "Dr." go to Starbucks, order a coffee, and then ask your barista to endorse your supplement. (I would think there's no shortage of people with PHDs in English who need $500.)
Or ask Dr. Pepper, who recommends at least 8 cans of soda per day for optimal health.
Also look into Healthy Directions. That company has a model that involves getting MD's onboard.