Where to buy kurogoma stuff?

I'm not looking for souvenirs, but just like those 100-200 yen snacks you can find at convenience stores of dango/daifuku, but the kurogoma version. Last year 7 eleven had these kurogoma paste filled sesame balls for like ~200yen each, but that was available for a few weeks. I also don't see those chinese kurogoma balls aka tangyuan in the frozen section of stores either. Why isn't kurogoma desserts not more of a staple in konbinis/supermarkets? Is kurogoma just not that popular? There's always redbean, kinako, matcha stuff, but rarely any kurogoma… I've been to major konbini chains, LIFE, Olympic, seijo ishii, AEON, summit, and it's all the same.