Someone else will probably come along with another option but my first thought would be to use and image editor to create texture. Here I started with a middle gray square, added noise, and then adjust the color. With a little more effort they could look better. I expect something like this could pass for a floor like you show in your images unless you are going to be doing renders down at floor level.
I use PaintDotNet although I’m sure you could do the same with PhotoShop or GIMP or whatever. FWIW, you could probably also use some layering in the image editor to maybe add some black or white specks.
I’m happy if it helps you out. I’d like to see your results in Vray if you’d care to share…