Hello,
By definition, you can't.
One product can have just one vendor.
But you can use the HikaShop characteristic system and the special "vendor" characteristic to create "variants" for a product, each product for each vendor selling that product (which allow each vendor to have its own price).
Otherwise, HikaMarket provide features regarding "sales repository" which is based on an HikaShop item custom field allowing the customer to select its "sales rep" vendor for the item.
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.