Ian Dairin‘s series KatZ is a frequent part of the magazine, and he’s been known to draw Spirou fanart.
Bercovici is another artist who draws one of Cauvin’s series for the magazine; in his case Les femmes en blanc (“The Women in White”) as well as several others.
Bédu draws the Cauvin-penned Les Psy (“Shrink” or “Shrinks”; I’m not quite sure) which runs regularly in the magazine.
Perhaps you don’t think one piece of fanart a week is enough? In that case, you might want to check out InediSpirou’s fandom blog, where Emyla picks a different piece every week (Monday’s apparently). Here’s one of Seccotine (Cellophine in Cinebook’s English translation) from a couple of weeks back:
Jannin is a long-time contributor to the Journal, and apart from his own comics he’s also been in charge of the recent color restorations and recolorings of some of Franquin’s Spirou stories.