http://www.derbymercury.org.uk/mountain-biking.html They’re a friendly lot, used to be a mix of lost roadies right upto a guy who rode a Yeti AS-X, looks like it’s more of the former now though judgeing from the pics.
Depends what you’re after really, TBH most of the stuff locally is CX/Gravel/Singlespeed trails, interspersed with the odd yoofs DH track or techy bridleway, but they’re the exception rather than a rule. The magazine actually did a route guide around Ticknall years ago, IIRC Cy from Cotic was on a prototype Hemlock.
Even the north derby riding is more of the same.
Fortunately you’re only minutes from the Peak. Probably 30min to the White Peak and an hour to the Dark Peak. No idea about organised rides, but those would be my preferences for a Saturday ride.