Ah.. different writing quality, I see. Not really a pen expert myself.

https://www.reddit.com/r/pens/comments/1cnvxcs/itoya_gpr7bkbp_alternative/

I cannot find anywhere on the planet, let alone just USA, that has those specific cartridges in stock. One online shop FCI-Tech claims to have them, but very likely doesn't based on other reviews of the company.