You can email Taito directly (OVS@taito.co.jp)and ask for a purchase invoice.
Taito sells two types of stools, the classic (43cm) here...
490139510 TT STOOL T50(43CM) BLACK LEATHER ＠JPY5500/pcs 5pcs/CTN JPY27500/CTN *Lead time 30days
New Vewlix style (48cm) here...
490652810 TT STOOL T50(48CM) BLACK LEATHER ＠JPY5500/pcs 4pcs/CTN JPY22000/CTN *Lead time 30days
Both of these are listed in JPN YEN, and the price does NOT include shipping, bank fees, currency conversion fees etc.