I believe Paul wants an original US 1 sheet.
I collect ONLY original posters myself and it’s not too hard to get up to speed with them. Obvious signs are the issue codes which appear in the lower corner. Also, many original posters were issued as folded until the mid-80s, so you will find a mix of folded and rolled versions.
While original posters can be found in NM condition, you’ll find they’re less minty than fakes/reprints, which go for glossy white borders and are pretty easy to spot. These days the fakes can get really good, with some even replicating fold lines etc but just do a little research.
Ebay has a lot of reputable sellers and you’ll find other great online retailers like Cinemasterpieces and Posteritati. Just expect to spend several hundred dollars for an original. If it means that much to you it’s a nice thing to have for sure.
I personally can’t stomach cheap reprints, mainly because too many people out there are simply stealing art. It’s really sad how prevalent it is and if you’re up for giving money to these kinds of sellers then you may as well just print out your own at home.