that's actually so genius I'll be using that in the future, for sure.
I just looked through IKEA and didn't see it, but there were some that were awfully close. this Daydream Hour was published in February 2021 and drawn even earlier, so I don't know if their current catalog goes back that far, or how ubiquitous IKEA is in japan? like even if it's there, I don't know if it's the first place someone would think to look for a 3D model of a couch.
the other reason I think it might not be IKEA is the shape of the couch's legs. IKEA almost exclusively uses scandinavian/mid-century style design, and (especially in the mithrun drawing) the legs look ?? carved?? like not just cylinders or rectangular blocks.
considering she had someone make a kensuke 3D model for her, she could have done something similar for her other 3D models, and KNOWING she uses csp makes me think it'd be most convenient to just stick with that than mess with a ton of other software