I buy sponges like that directly from China.
https://www.fasttech.com/p/3367200 (Not affiliated, just in general a satisfied customer)
I agree that they are very useful and user friendly.
The ones I buy are marketed for fingernail care. Thus, all sides are very fine grit and extremely useful for very light sanding and then polishing your surface back to gloss. (I’ve used them on (vintage) plastics, steel, stone, acrylic, ebonite, brass all to good effect)
Last time I bought them when the site had a sale; 68ct a pop. Have so far used up one, broken in another one at work and one at home.
Will get more some time.