If you look around, you should be able to find a small detail / touch-up spray gun, either gravity or suction feed. These use between 1.5 and 4 cfm and will work with your small compressor ..... though it would be marginal. Further, you really should have a good air regulator and water trap, even for small modeling jobs. Your small compressor will run most of the time when supplying any spray gun and soon, the tank and lines will be loaded with water and you won't like that in your finished product. A water trap will prevent this and they can be had at a low cost at a store such as Lowes.

There really is no substitute for an adequate compressor but there are hundreds or guns out there that require less airflow than the one you have. I have a couple of gravity feed, brand name touch-up sized guns that work well for model use but my all time favorite is still my 40+ year old Binks 15 suction feed touch-up gun. All these guns have between a 4 and 6 oz. cup and are easy to handle for our use. All have fairly large fluid tips (1mm or larger) and will accept fairly thick epoxy or urethane primers, paints and clears. I would always recommend a name brand gun over one of the cheap Chinese, discount tool store guns if for no other reason than parts availability. Try buying a fluid packing for one of the cheap guns sometime and you will know where I'm coming from. Some of the cheap guns work quite well though and like many cheap tools, you can throw them away and get another if the first one breaks.

Look around and you should find what you need without spending a fortune. If you start painting very much, you'll quickly find the cost of materials going through the gun far exceeds the cost of the equipment!