There are all too many companies out there on the net, that have such motors. The next questions you need to ask, are what type of gearmotor? Do you wish a worm, spur, planetary etc? I can point you to specific companies, if you can specify the mechanical characteristics, to accompany your electrical specs.
Well, this is a difficult scenario! I myself, in the development of prototypes, have run into the very same situation that you are in now. I did the same thing that jbartos has suggested, and that is to go through the many, many, many...companies that sell such motors, through the Thomas Register.
You stated that a worm drive will "do", but is a worm drive really what you "need"?
An example: Worm drives tend to be larger, and draw much more current than spur gear type drives. I needed a motor assembly that has 5rpm @ 120 in/lbs. In spur gear assemblies, I could get this easily for around 50 dollars, in a very small package (3" X 2" X .5" gearbox). Current draw was about 1.2amps.
In searching for a worm gear alternative, to get the same results, the motors were HUGE, drew an enormous amount of current, (9 amps +) and were not nearly as easy to find. They were also several hundred dollars.
So, out of concern for you, I ask you, do you really need a worm gear drive for your application? You could, in a smaller package, even with an added magnetic brake, and for less money, use a spur gear motor drive. It will cost you less, it will draw less current, and you can add features to it, all for less than just a worm gear drive.
I don't mean to pry into your business, but are you developing a production run product, a prototype, or a hobby project? In any case, don't spend the money on a worm drive if it is not needed!
Look online for this company: