Getting access to non-public information is, in fact, not illegal. Using non-public information
from sources with a fiduciary duty to the company is illegal. You can
create non-public information in arbitrarily complicated ways. For example, you could hire a satellite firm to put spy cams over every WalMart parking lot and then count the cars in them, then produce a report about WalMart's quarterly sales weeks before the market heard about it from WalMart. That report is non-public, right? Totally legit to trade off of.
Satellite analysis of WalMart parking lots is, by the way, an actual thing. (It is an actual thing which suggests, among other things, that if you are a retail investor, you should strongly question whether you really have insight into companies which professional investors do not have.)