I know that one of the official DnD map artists, Mike Schlay, sells map downloads. Mostly regional maps, some of the cities. If there isn't an appropriate map in the marketplace you should seek out the official artist's shop or fan-made free materials like what Kris just posted. Many of us have made renditions of parts of Faerun for our personal use. I made Icewind Dale maps for my use for example. Obviously not in the Roll20 shop. Or just buy the package? If it is a package Roll20 definitely has, you could always submit a ticket and request a map-only pack for that series. They might make it possible. :) However, failing that, contacting the original artist is always your best bet... they will know where or if it's available separately. Who knows, some of them might even make their own Marketplace listings if they know their work is interesting to the audience here.