Diamond makes a couple of 6/2/70 SMA antennas. The are hardly stubby. SRH940 and SRH999. They are 17.75 and 19 inches. A stubby antenna that would work on 6 meters is not likely. Any 6 meter HT antenna is quite inefficient.
With you being new here to this site, please don't get upset with some negative comments that may come your way.
My first suggestion is to go do some homework and find out just what a quarter wave antenna length is at the different bands your asking about.
After saying that, having been in this field for a long time, stubby antennas are not much better than a wet noodle. The results of your antennas you try to use will be in direct relation to their length. A short antenna results in a sort receive and transmit distance. This has been proven many times in the normal use of Public Safety portable radios. The boys out in the field don't like the normal flex antenna on their portables poking them in the armpit. But when your out in the field and find yourself in a pile of crap, you will want to have your radio work when you mash the PTT button and cry for help.
The stubby antenna will work in four real close to the repeater antenna or inside a shopping mall with a bi directional radio system installed inside the building. However, if your out in the field and getting close to the fringe of the radio system coverage, you will be SOL.
This may not be what your looking for an answer, but this is the reality of how the radios and antennas work. If I had to put my life on the line, I would want the best antenna I could find. Not rely on a stubby antenna.
Now back to what your asking for. I know it's in the ham band type application, but the same thing applies to the ham bands as it does in the real life Public Safety radio systems. Short antennas don't work well. I have a better word for a description, but I would rather keep on the good side of the moderators.
Plus the use of an SMA connector is like saying you antenna is relying on a toothpick to hold it upright. The SMA connector are not made to stand up to any abuse. You want an antenna to last, but a decent connector on it and the radio. Even a BNC connector is not what I would call rugged.