I'd have only one solution that also encourages MultiPlayer/MMO interaction :
- while docked at the same Station/Outpost etc., permit Player-to-Player trade
Any Player can mark Materials and a trade limiter for all Elements/Materials/Data (things offered to trade away + things the Player is requiring/accepting + optional "Credits accepted"), "offering to trade" is broadcasted to the Station Services.
While any Player docked with this offer enabled, Station Services display something like "Materials Trading of Opportunity" which other Players can check for.
That way and intuitive/hassle-free, Players can do limited ad-hoc trading with random others while docked.
Fixed Trade ratios or the Credit fee as set by FDev.
So dock at any busy place and see what's in the pool.
Alternatively, Players operating in a Group/Power/PMF/Squadron can do this in a somewhat organized manner.
Pros - no fixed requirement to visit Mat Trader, a positive and beneficial/logical social/MMO aspect (meeting random strangers can now pay off)
Cons - you might not get what you want nor the desired quantity (merely an Opportunity); Players aren't Mat Traders with unlimited stocks after all, which remains their unique Quality