A note on this part:
EDIT
This is how you find where the stuff is sold: use this tool http://www.elitetradingtool.co.uk Go to Search, in Search Filter click Commodity, then Station Selling, choose commodity, type in your current location, select 25 ly range, small ship, and then search).
I find it more rewarding to figure out and/or search for the commodities myself. Yes, it takes some time, but if you take notes of which commodities 'your station' BBS ads need and check those commodities while doing 'deliver this there' missions, you find sellers easily enough.
Also, in the trading screen, 'imported from' and 'exported to' lists are usually helpful. Mind that sometimes they can be off, or even the polar opposites.
Another tip for learning the economy is taking notes of which commodities each economy type (station) needs and which they produce - also bear in mind that some for example high tech stations don't sell (or buy) stuff that others (or most of them) usually do.
That said, doing rare items runs I quite soon succumbed to the list instead of trying to find new rares myself:
https://forums.frontier.co.uk/showthread.php?t=63119
Remember: It's not the destination, but the drive there!
