Agreed. While it makes sense that a faction would withhold their best equipment to the public for the sake of their own fleets, and to incentivise people into joining up, there's always a way to grease the wheels.
On bribery, I think it should have a more compelling trade-off than just higher costs. Rather, it'd be cool if it were linked to black market suspicion or had a similar system of its own. You can bribe an official to allow you access to that equipment, but if you're caught with that equipment, commodity or ship that by all rights you shouldn't have access to, it'll damage your relations with that faction. It'd be even cooler if it were done without subtlety, and discovered that an official accepted a bribe, that they were then replaced by someone with higher loyalty to their faction. Some station commanders could refuse bribes, some could refuse and view you in a poor light damaging relations, some might only accept them if you come in with the transponder off.
So another alternative to a commission requirement could simply be becoming very friendly with that faction. If you've jumped into fights to help their fleets, brought them food in times of shortage, ran missions and hunted bounties for them, I don't see why most would still then refuse to allow you access to their higher-tier stuff - favourability could function as a currency in this sense. You've done X favours for <faction>, so they'll allow you access to Y value of equipment/ships. I could go either way with their top-end equipment and ships still being locked behind a commission though, to retain that incentive for the commission - which would still allow you access to their lower-tier stuff earlier than getting way over on their good side.