Yea G180-18 has some nice modules, also Asellus Primus, Aulin, Styx and if you want some of the rarest and most expensive then Yanyan which is near Asellus Primus is a great station to upgrade. The shop changes inventory when the hour changes to the next hour and the best time to buy upgrades is in the early morning (earth time) because any other player at that station at that time can buy them from the outfitters and take them off the list until they possibly become available the next hour chap.
I am finding B5 and A4 modules for my Asp very easily at Yanyan, at a reasonable 1.7 million to 5 million, obviously the modules will be cheaper for smaller ships there than what my Asp modules cost chap.