Finding 18% grey Matte ball

[Duca]

i everybody,
I'd like to buy these accessories for reference HDRI image (Rendering):
http://akromatic.com/gadgets-info/
How you can see, they are extremely expensive...
I've already a Chrome ball and a X-Rite Checkebox and I need now, only a 18% grey matte ball.
Where can I buy it?
Another possibility would be to paint a ball but in this case, which kind of grey (color formula) I've to ask to have 18% neutral grey?

Many thanks!

Duca

 

[Slaters]

Buy something like this.
http://www.krylon.com/products/colormaster-primer/

Spray it on a flat material the same as what your ball will be made out of.

and then photograph next to this.
http://www.bhphotovideo.com/c/product/101853-REG/

And use the difference between the two the calibrate the wrongness of the primer. (primer will be a bit brighter I believe)

Paint your ball. And always remember to keep it clean.

 

[Duca]

Thanks S,
but I'd like to found the right grey painting rather than calibrate tow different greys...