All major supermarkets in Dalian sell soft-shelled turtles (New Mart and Carrefour definitely sell them). There are many turtle brands with different prices, but the cheapest ones are all in 30 yuan/kg or above.

If you buy a turtle in the supermarket, the store will kill it for you directly, so you don't have to do it yourself.

Turtle black chicken soup is a great tonic. You can ask them for recipes at the supermarket counter where you buy turtles.