Drain oysters, reserving 1/2 cup oyster liquor; set aside.
Melt butter in a Dutch oven over low heat; add flour, stirring until smooth. Cook 1 minute, stirring constantly. Gradually add reserved oyster liquor, whipping cream, and sherry; cook over medium heat, stirring constantly, until thickened and bubbly.
Add oysters, ham, salt, and pepper; cook over low heat 10 minutes, stirring frequently. Serve over toast points.