No idea if this is the case anymore, but many NY Public Libraries had "Stacks" where they kept lots of magazines going back to the 1970s. I havent checked for at least a decade, but that was a lot of fun -- we'd go there and look at old computer ads from the 1980s. They would have a binder per decade -- giant thick binders.

If you're willing to put up with the hassle, you could find them on Microfiche for sure. I've found newspapers from the 1700s in NYPL's microfiche archives https://www.nypl.org/about/divisions/general-research-divisi...

Short answer: probably not. Discussion from almost ten years ago:

https://news.ycombinator.com/item?id=14472265

There is the Internet Archive, but the scans aren’t great:

https://archive.org/details/omni-archive/Best_of_OMNI_1_1980...