Ok - went to Harbor Freight and looked at their guns. Here's a brief commentary on what they had on the shelf. I should also say that I tried to stay as low as I could on the SCFM requirement scale to accommodate your compressor. All of them came with a 1 quart aluminum cup. None are HVLP as the only HVLP I found on the shelves were detail guns. Those aren't real big air hogs and might be worth a try, but these are all standard siphon guns of the Binks model 7 design.
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gun felt like junk. I tried several of them and all of them had rough triggers. I suspect they have a really poor packing and will be nothing but trouble. I'd stay away from this gun.
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gun seems pretty good, but it's quite high on the SCFM requirement. You could probably shoot this gun with as low as 8-9 SCFM, but a compressor that's putting out 4-6 probably isn't going to cut it. Gun construction seemed to be quite acceptable for the price point. Smooth trigger action and adjustments. Without shooting the gun, I'd probably take one home on the expectation that it would make a reasonable cheap Binks model 7 knock off. Maybe not something I'd shoot clear coat with, but then again I don't use my Binks for clear coat either. Should do all non-latex paints and stains with good results.
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gun had a surprisingly smooth feel and action. It's an ABS body but for non-autobody work that might not be a big deal. The air cap and nozzle are the same ones used on the above gun. The needle, seat and packings appear to be the same as well. For under $15, I'd probably try one of these for your use. They want 9.5 SCFM, but a good stout 6 SCFM might well work. Again - for the price it's easy to take the chance.
Let me know if you need more info.