First of all, hello to everyone! I write to you from "Bel Paese", Italy! And I apologize for English, but being not very good at English I'm using Google Translator. Now the question is: Why does not an Ad Support exist? Has Riot been conceived in an Ad Support? If yes, how has it not been "created"? If not, why? Thanks to everything, and have nice day! [slayer-jinx-catface]
Edit: I apologize if I was wrong "place" for the post.
Traditionally it makes more sense for a support with the ability to poke to be ap ( a sort of support mage if you will ) because an ad mage doesnt really make much sense without said champion being played as a carry, so not only would it be difficult to design but it would actually have a negative impact in the early game. An AD support would allow opposing laners to just run armor in runes and maybe rush ninja tabi or cloth armors just something for the early armor, and with no ap damage coming from the support an opposing lane would have a significant advantage in the 2v2. The only exception to this would be Corki as his passive is currently converting 80% of his damage into ap damage.
Do you mean ad carry-type support? 
Basic attacks don't provide any utility (most of the time, I'm ignoring stuff like Frozen Mallet) while abilities can provide utility, and supports are there to provide utility for the team. Therefore, supports rely on their abilities to provide utility. That's why when some traditionally AD Champions go support like Miss Fortune or Lee Sin, they either build AP (Miss Fortune) or they build tank (Lee Sin). With those builds, those Champions can provide the utility their team needs. If Miss Fortune went with a full lethality build, then she wouldn't be providing her team with good utility because she'd be relying on her auto attacks, not her abilities. There are a few supports that do a lot of AD damage like Pantheon, Lee Sin, and Illaoi, but if they're building full AD then they're doing their job wrong. Also, there's a reason you'll almost never see these Champions as supports. So many other Champions provide better utility than these Champions.
well in theory 
can be an AD SUPPORT
he has a shield/aoe slow, his ult and trap a target for the adc , his flag gives his adc bonus attack speed he has armor shred , he has enage, knock up , gap closer
The problem with an AD support is that they likely wouldn't stay a support. A kit that allows an AD champion to support would likely become a jungler with powerful ganks making them rarely seen as a support.
So technically, an ADC.
I usually get 15 ad runes on support Sion. Tend to pick up at least Frozen Mallet before midgame. Does that count?
