No non-sus 29er mtbs?
The 29ers without front suspension exist, but they are a bit pricey since they come from niche manufacturers. Many people want SS drivetrains since they want pure simplicity.

Surly ships some of their complete bikes such as the Ogre as rigid 29'ers (the Karate Monkey can also take gears).

There are some other options though. One common option is the Kona Unit which has a derailleur hanger which you can order from Kona as seen here:


Or an internal gear hub as seen here:


Note that both these options require at a minimum a new rear wheel for the Unit. 

Also, note that Surly sells their rigid forks as well as do companies like On-one and what not, so you can get one installed after market. 

Finally, yet another option: Get 2 bikes (something cheap and not likely to be stolen for city use, one for trail use).