Retailers are classified as either boutiques or mass stores.. You need to specify which and what industry. If it's in fashion, your best bet for boutiques is visit the store. You can try cold calling but from experience visiting the store (in person) is best way to go.
As for mass-stores, you have to find a way to get hold of the buying office (many are listed on their website "Abou-Corporate" page).. Or you can go straight to one of their branch stores, connect with an employee and juice them to give you full name of the Dept buyer. You can usually figure out email from there "[removed to protect privacy]"
That said, more info of your question is needed to give more accurate answer.
Please note, most retailers don't buy into "undeveloped products", they need to see and feel something before making their considerations.