If you are really looking for a good finish on all your HBG pieces, you could buy a couple small cans of differing lacquers and test each one. $20 should get almost 3 cans worth. It may be a waste to some degree, but at least you can know for sure which one works best.
I have a flat Testors lacquer/sealant spray that I used on Tall Paul’s finished pieces. Granted, these were painted first, so the effect may be thrown off. However, I will say that I did not observe any level of gloss on the HBG or OOB pieces after I applied it. It was quite flat as advertised. FWIW.