Wg słownika Oxfordu:
- We buy our fruit and vegetables
at the market. > w znaczeniu: an occasion when people buy and sell goods; the open area or building where they meet to do this
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on the market > available for people to buy, e.g. to put your house on the market. The house came on the market last year. There are hundreds of different brands on the market.
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in the market for sth > interested in buying sth, e.g. I'm not in the market for a new car at the moment.
I jeszcze TheFreeDictionary.com:
in the market
Interested in buying: We are in the market for a used car.
on the market
1. Available for buying: Many kinds of seasonal flowers are on the market.
2. Up for sale: They put the family business on the market.
Moim zdaniem w przykładzie, który podałaś zastosujemy "on the market". But correct me if I'm wrong.