While Dave Sim is the best known participant in the Cerebus experience, he had a collaboratorL gerhard, who drew backgrounds in a richly detailed manner. Gerhard (he uses one name) he been making a comeback of sorts—although he has been doing illustrations right along—with convention appearances and prints, and how he’s selling some of them online. And they are pretty amazing, like the above, which recreates the cover of the High Society collection.
And a couple more. Prices are in the $50-70 range (I guess that’s Canadian.) Anyway, lots more in the link!