At this point, both Kush and OG are effectively just marketing terms that dispensaries and breeders throw an any strong indica-like plant. Many of them are related to the famous "OG Kush", but many aren't. Also, this strain has been so widely hybridized by so many breeders that many strains that do not have "OG" or "Kush" in their name are genetically related to OG Kush.
So depending on your point of view both terms "OG" and "Kush" are real, or neither one is.
In answer to the original question, yes, there is a famous strain that goes back to the early 1990s called "OG Kush", and that's probably what you're after.
The strain was largely passed around as clones, not ceeds, and for that reason many different versions ("cuts") of the original still exist: SFV (San Fernando Valley) OG, Tahoe OG, Ghost OG, etc, etc.
At this point, the strain has been so widely self- and outcrossed that I think there is a bit of room to argue what is and isn't a "real" OG Kush now. For example, some might say that if you're buying it as a ceed, it can't be a "real" OG Kush, because those are "clone only". If you are in CA or elsewhere where you have the ability to get clones, I'd say do that.
If not, there are a WHOLE bunch of breeders now that offer "OG kush" ceeds that represent various self pollinations (S1s) and/or crosses of the originals, and are supposed to mimic them. From lack of experience, I can't tell which ones are the "best", but you can try:
Reserva Privada: OG kush and OG Kush #18 (you can probably just end right there).
Cali Connection: Larry OG Kush, Tahoe OG (and probably 3-4 others that are other permutations of OG selfs and crosses)
Dinafem OG Kush
Granddaddy purple OG Kush.
Humboldt Se-ed Organization OG Kush.
For hybrids of OG Kush cuts with other things, there are way too many to list, but in addition to above consider Gage Green OGs, Karma Genetics OGs, DNA Genetics Lemon OG and OG LA Affie, etc, etc.
