or any API at all
Then these aren't programmers.
Much of application programming today consists of making calls to multiple APIs. A competetant programmer should be able to pick-up most APIs (provided there is decent documentation) pretty quickly. If they profess lack of knowledge or skill about APIs, run the other way!
Anyone suggest places to find these programmers?
If you feel you really need somebody who already has experience with the Adwords API, you might want to check the Google Forums Adwords API Forum. It's also a good place for your programmer (if you get one elsewhere) to get help with any problems.
The Adwords API is not terribly difficult to use or understand. If I were in your position, I would make sure that you get somebody who is competant in your core technologies. (i.e. those tools, languages, techniques, etc. that you are already using). A good programmer should be able to pick up the Adwords API quickly.
You mentioned PHP. You probably have more need for a programmer who is competetant in PHP than one who is specifically an expert at the Adwords API. Experience with SOAP will be helpful, as the Adwords API uses SOAP. If you already have a PHP programmer or programer(s), and they are not overloaded, they may be the best bet.
If you don't routinely hire programmers, then you need to step back and learn how to hire programmers. Frankly, you need some degree of technical competency to do this. While it might be an old-fashioned approach, a temporary hiring agency that specializes in programmers may be your best bet. They can ferret-out from you what technologies the programmer will need to be familiar with and have a pool of people that they have experience with and can make an appropriate match.