Thanks, you’re the fourth to link them to me. 
It was also shared here: Pokémon Center Japan News Thread - #9 by koala.
I’ve tried buying the items through Buyee. When I initially looked about 12 hours or so after it went live in the online Pokémon Center, the Seviper shirt and towel were out-of-stock. Ironically enough, Buyee was able to buy those two items only, and everything else was out-of-stock for them.. When I later checked, everything was in stock again, so I tried through Buyee again, but unfortunately they cancelled that second order.
I did buy a cheap listing of the Notebook on Mercari yesterday, so I now have that one also incoming to my Buyee warehouse. But I still have to get the other four items featuring Seviper (other shirt; tumbler glass; clear file; and tape roll).
They do still seem to be in stock on the Pokémon Center webshop, so not sure why it wasn’t for Buyee. 
I might try a different middleman service tonight for those four items.
Greetz,
Quuador