In general, for cultivation of macro algae there are two common methods one is fixed rope method another one is floating raft method. In both methods we are using either mangrove stakes or bamboo poles. In earlier coir ropes were used for inserting the seed material ( apical fragments)

I recommand whilte vinglon strain for seedling spores. Attachment is my publication which assessed the different effect on the seedlings of Saccharina japonica with white vinylon and brown palm strains. This article is in Chinese with English abstract. I hope it can help you.

The providers all I known are in China. Maybe you can contact with Professors who do research in seaweed breeding in Korea. They may know someone in Korea.

Thanks so much all for your answers!