reduced acrylics?

Some paints need to be thinned to use an airbrush. I suggest a trial and error method with all paints. You will find that paints made by the same manufacturer have different thicknesses so the thinning is different. Some need no thinning at all.

Would you have any idea if Tamiya paints would need thinning?

I sometimes thin Tamiya paints but usually only if it needs it. I find that Tamiya is pretty good to shoot right out of the bottle. Once again it really depends on the colour as to whether or not it has the right consistency for spraying. The colour flat black is one that I find never needs thinning and I use that as my guide. If it's flowing like the black, then I know I'll have no problems spraying it the way it is.

Try Isopropilic alcohol, work find and is cheap. The proportion depend of the color. Mix in a soda lid plastic bottle, the alc. and the paint, use an eyedrops tube or a pippete, Testor sells set of this and they are AAA, test the density with a toothpick and when you are satisfied with the results transfer the same proportion to your airbrush cup or bottle. I read too, that adding a bit of gloss finish, help to reduce that the paint clog the nozzle of the AB. I didn't tried yet but I will. Good luck.
Feria

I have had great success with Gunze Aqueous hobby color.I simply add 4ml-5ml distilled water,and 1ml Gunze Mr. Retarder to the 10ml bottle of paint,Works for me.Give it a go,but test it first on a peice of sheet plastic before you use it on your current project.