I made this bracket to hold my 5 lb. CO2 tank to the wall as I didn't want to risk it falling over.  While the wall portion is very specific to my location, I figured I would post it as others could easily modify it for their situation.  

I don't recall all of the specifics when I printed it.  I do recall I used thicker walls than normal (1 or 1.2mm), and the infill amount was in the 20-40% range.  Wall attachment was with drywall screws and countersunk washers.  Unfortunately, I don't recall the specifics of the hardware for the bracket itself, but you should be able to pull measurements and find what you need at a hardware store.