Dave from KMI here... I've been pondering your question about finding a case for your 12Step and I think I may have a solution....
The majority of bags I have looked at are at least 18.5" long, which will easily accomodate your 12Step or a SoftStep. (at least in theory). Check out VicFirth:
I'd go with the Standard Stick Bag. Thankfully, our StepProducts are hyper durable, so a bag should do the trick. If you want a hardshell, i know Coffin Cases makes a "coffin" shaped hardshell stick case, but their website doesn't give any information
If this works, let us know.