Hi,
I think that the best way to do so is to use the product limitation.
The "product limit" feature is provided by commercial edition of HikaShop (HikaShop essential & HikaShop Business).
Thanks to that, you can create a rule to have a limitation of 1 on the specific product for the period "forever".
demo.hikashop.com/administrator/index.ph..._hikashop&ctrl=limit
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.