Not really. The closest is "三角のおにぎり" to describe the shape. Onigiri have been made in many different shapes over time, including a round shape and the occasionally clever shape that a creative mom might try to make. But many people now think of triangular ones as the normal mode, so you wouldn't need to say anything other than "onigiri" to imply the triangular shape. You might need to use special terms now to imply non-triangular shapes, the same way you might describe a "square hamburger bun" in English.
I'm not entirely sure if it's the shape or the packaging that you're concerned with identifying. However, unless you're a packaging industry professional, there's probably no need to make that distinction, and therefore there's no commonly used term to describe that special packaging. The fact that you got it at a convenience store or supermarket will be enough to imply this kind of packaging, so you could just say "コンビニのおにぎり" if you got the product at a convenience store.
In Korean the term you are describing, kimbap, without the "samga" modifier, usually implies a rolled sushi-like item which is called makimono (巻物) in Japanese. This may explain the need to use the "triangular" modifier in Korean.
As a food geek, I can attest to the credibility of the onigiri explication here: