I don’t think I understand the question. Are you wanting a link? Or are you asking like what the best kind is? I’ve purchased fake black suede leather there. There are many kinds. Nobuck, silk, cotton, paracord, etc

You can buy the actual Japanese silk from Nihonzashi out of Florida. Also, I believe cottontailcustoms sells some.

eBay has ito sageo as well. Amazon has a variety… Search “sageo for katana” on Amazon

Good brand:

https://smile.amazon.com/dp/B07C7ZT4C1/ref=cm_sw_r_cp_api_glt_i_T44NPDGXSKSMN9GXMV6D