Actually you just need to visit a station that sells the illegal commodity and look on the commodities market.yeah, you can know that if you go there with this goods.
But we haven't a board with all governements and laws?
Like "Feudal allow weapons but no drugs, democracy allow drugs but no slaves etc"?
The commodity description of every commodity that has a supply > 0 and every commodity in your hold now includes a paragraph that details exactly which government types it's legal in.
Obviously for most commodities this just says "legal everywhere."
As for the game being empty, I meet other cmdrs literally every single time I play - I even passed by two random explorers on the neutron superhighway last week while Buckyball racing (in separate systems) - I initially assumed that both would be fellow racers participating in the same event, but neither was. I only had time to exchange quick hellos and one friend request as there's no time for idle chat during a race, but I was very surprised as I've only encountered explorers at Sgr A* before, never at random systems outside the bubble.
@Rootsrat: the problem with the PMF insertions into rares systems (only the potentially illegal ones) is that:
a) in the past (e.g. with Noti) the PMF automatically gained the main station, which suppressed the rare with zero BGS gameplay involved.
b) Since it's the home system the PMF can never be driven away from the rare good.
The Noti master chefs getting suppressed in that manner was especially annoying as it was a CG reward to insert it in the first place. Running 4 tons of Aganippe Rush at a time between systems so close that there's no point tea-bagging.
And Wolf Fesh was the best (ie most illegal) rare narcotic - instantly suppressed by the insertion of the biggest Xbox One player group's faction.
LL's 20 PMFs based in rares systems is a little misleading though, as most of those pre-date the ban, some (e.g. SEPP) are adopted NPC factions that pre-date official PMFs, others e.g. Hutton Truckers are large established player groups that pre-date PMFs, and some of the races (e.g. Silver Sea Rum, Hutton Mugs, Buckyball Beer Mats) were invented by the player group / faction.
Plus for an 100% legal rare commodity it doesn't matter who controls the system anyway.