Hello,
I am looking for more VFX images / textures to prototype and create effects with.
I am not looking for flipbooks. I am rather looking for simple image masks like swirls, stars, projectiles, bursts etc.
Do you know where to buy these images as a collection / library / pack of >1000+ with a good quality of at least 1024² pixels ?
Best
GreetinGs
I’d recommend taking a look first at the free resources out there. Gumroad has a few quality textures!
Also, you can check out Kenny’s particle texture pack, it is 100% free, no attribution required even. The textures are rather generic/simple, but they are super good. I even used them recently on some assets I made for the asset store incidentally.
Niels Dewitte also has some textures on his homepage:
It’ll be hard to find 1024² textures throughout as it is (has been) not common to use textures large than 512² for simple shapes. Most of the time you can even get away with using 128² or 256², depending on the size of the effect. If your sprite is not large than 512px on screen, there is no benefit of having a 1024² texture.
You can always manually scale those up in an image software and slightly blur them to get rid of artifacts.
Or you create your own, e.g. with this tool:
https://mebiusbox.github.io/contents/EffectTextureMaker/
On a side note: Having a massive library can be nice, but it’s quite likely you’ll be using the same shape textures over and over anyway. At least for 90% of your fx. This is all the more true for noise textures. Just having aving about 5-10 high quality noise textures will set you up for life 
Thank you @Nokdef and @TobiasTobasco. Helpful info.
The only additional particle / sprite pack I found on Gumroad is:
But it seems not very useful for the amount of money.
I also searched at Artstation… without luck.
Honestly, I am very surprised that there isn’t a bigger market… yet.
So if you find offers let’s collect them and share these here in the future. 
I bought this pack: https://www.artstation.com/marketplace/p/V9Kj/100-seamless-noise-textures-for-vfx
and can recommend!
But yeah, you are right, it is not a very big market.
Oh, this looks useful for only 1,45€. Thanks @Nokdef. The clouds library of this creator also looks useful.
I found this particle library at the TimelineFX website.