Haven't found it yet, but I did find Sephora's Marble Art topcoat, which claims to do the same thing.
For the price of 5,14 USD I thought I give it a try.
As base for my nail art I used two polishes also purchased at Sephora:
Left: Sephora - 84 Full moon party
Right: Sephora - 72 Tomorrow, detox!
Both nail polishes have a simularity with metallic polishes.
The left one can be described as a dark purple with multicolor glitter.
The right one is a petrol color with silver glitter.
I started with two coats of the purple polish and then placed some randomly areas of the petrol color.
After this simple base let's get to the most important part of this post:
Sephora - 07 Marble Art
The topcoat itself has some simularity to watercolor paint.
I applied a very thin coat of this topcoat (too thick will just make a black nail).
It immediately starts to make holes in it. No perfect dots, but more random shapes, revealing the underlaying surface of petrol and purple.
I haven't used a topcoat, but if you're satisfied with the outcome, I think you should.
If you wait some time before applying a topcoat, some more marble art topcoat will be gone revealing more of your base color.
I think the nail art looks better the next day (revealing more of your base), but it all depends on your own desires and also your underlaying colors I think.
I'm very happy with the two topcoats I bought at Sephora (also see previous blogpost about Sephora's Tie Dye topcoat).
They've turned out better than expected!!