I need a letter to introduce my locally grown fresh cut flowers to florist.

Sell yourself and your flowers in person, not by letter.

I agree with WG. Bring a sample of your flowers to the florist, talk to the person in charge of purchasing, explain your pricing, and how much you can supply, and then leave them a card. A few days later send them a thank you letter for viewing your flowers, and let them know you're ready to do business with them.