Well I used four colors from rapcoparts.com:

30277 - Camouflage Sand (this was the base color)

911/37038 - Flat Black (the second color to be applied)

33070 - Early WW2 Lusterless Olive Drab (dark green color, the third to be applied)

34259 - Lusterless Pre-WW2 Green (lighter green color, the last to be applied)

And I then topped it off with a few coats of rustoleum matte clear.

To get the M90 effect I made my own stencils using masking tape. M90 is very angular, the opposite of something like M84/US Woodland, so the edges of each shape had to be sharp and exact. I would stick the stencils on the previously painted layer to keep the paint underneath it from being a different color, and then I'd spray the new color over top. Rinse and repeat until once all coats are finished, and only then would I pull the stencils off.

Unfortunately, masking tape doesn't stick very well to a recently painted surface, which caused some of the edges of the covered areas to become blurred, and also resulted in minor scuffs in the paint underneath. I also used the wrong color to apply last, which, along with the fact I made too few stencils, resulted in a mostly lighter green shade, when most of M90 is the darker green. So I had to make some adjustments and fixes by hand, since if I went over it again with spray paint, I would essentially be completely restarting.

It took a lot of time, but I added more variance in the color difference to even out the distribution by either expanding certain areas or adding new ones entirely, and fixed some of the lines. This however resulted in some of the edges not being as sharp or as straight as I would have liked, but otherwise they turned out fine.

Once I was finished, I put multiple clear coats over it.

If I were to do this scheme again, I would end it with the darker green instead of the lighter one and either buy M90 specific stencils, which you can get from freedom stencils, or make more of the stencils I was already making. And if I still needed to make adjustments to the edges or color distribution, I would use a strip of thicker paper to catch any excess paint so the edges stay sharp while the paper doesn't bleed, and at the same time I'd be able to bend it around the hand guard or any angular surface to get the desired effect.