noun
supplier; vendor; retailer; where one buys something
Refers to the place, company, or person from whom one purchases goods or services. Often used in business contexts.
新しいパソコンの購入先を探しています。
I'm looking for a place to buy a new computer.
この部品の購入先はどこですか。
Where do you buy this part?
販売元 is the seller or distributor, focusing on the selling side, whereas 購入先 focuses on the buyer's perspective.
Compound of 購入 (kōnyū, 'purchase') and 先 (saki, 'destination' or 'source').