TOKYO — In the four months that Seiyu Walmart, as the big American retailer’s stores are known here, has been selling low-cost Chinese rice, it has struggled to keep shelves stocked at some stores. A Japanese chain, Beisia, also sold Chinese-grown rice for the first time this year but quickly ran out.

Kappa Create’s sushi restaurants have started to serve rice grown in California, while Matsuya, one of Japan’s biggest beef and rice bowl chains, has introduced a blend of Japanese and Australian rice. Daikokuten Bussan, which runs discount stores across the country, says it would carry foreign rice if it could get a stable supply.

Prompted by declining incomes, as well as fears about radiation from last year’s nuclear disaster in Fukushima, a major rice-producing region, a small but growing number of Japanese consumers and businesses are doing the unthinkable: openly abandoning their loyalty to expensive, premium-grade homegrown rice and seeking out the trickle of cheaper alternatives from China, Australia and the United States that make it into Japan’s heavily protected market.

“I don’t think many people would have considered buying imported rice in the past, but that might be changing now,” said Kana Saito, 29, a part-time office worker shopping at a Seiyu Walmart in central Tokyo. She had wanted to buy a 2-kilogram bag of Chinese-grown rice, but it was sold out.