Hmm... I've added them all to my wish list on PaperbackSwap. I will keep an eye out though and see if I can find them on sale or used somewhere though. I found Yellow 2 volumes 1, 2, and 3 all available for download from the library and, seeing how oddly manga are often named, never even thought they might have been a sequel. Oops.

Thanks! I really struggled to finish anything the first couple months this year, but feel like I've found my groove again.