BEST～2000-2020～ is listed on Neowing , which's CDJapan's domestic site
https://www.neowing.co.jp/product/RZCD-77457
I think the reason why BEST～2000-2020～ is not listed on CDJapan is because of avex's silly export rules , yet again
If not why is that I don't see V6's final release & their final studio album listed on CDJapan , same reason as before as avex distributes their stuff
And yes BEST～2000-2020～1st press bonus item is a postcard