Plextor no longer sell optical media of any kind; any Plextor discs you may find are old stock.
If you want Taiyo Yuden CD-R media, you can buy Verbatim Pastel CD-R media, which is always Taiyo Yuden.
Some of the Verbatim Extra Protection CD-R discs sold in Euope are also Taiyo Yuden, but only if “Made in Japan” - they are in Taiyo Yuden style cakeboxes if you know those. I’ve only seen these in 50pc cakeboxes but they might exist in other packagings. There are also Verbatim Extra Protection CD-R made by CMC and Prodisc (maybe others) so you’ll have to be able to check the actual packaging to be sure.
As an alternative, I suggest anything Verbatim marked as AZO (new style) or Super AZO (old style) e.g. with the Crystal surface. These will probably all be Made in India now and not as good as they used to be when Made in China or Made in Taiwan, but still better than most other CD-R media IMO.