Unfortunatley, the very high-fat cream you are looking for is very hard to find. Fortunately, there is an alternative that adds no additional flavor to whipped cream. It is often used by good pastry shops to top cakes, fill eclairs and pastries, and won't melt in the sun. This wonder product is stabilized whipped cream. Here is one recipe for it.
Stabilized Whipped Cream Frosting
2 tsp. unflavored gelatin
8 tsp. cold water
2 cups heavy whipping cream
1/2 cup confectioner's sugar
1 tsp. vanilla extract
Chill a glass or stainless steel bowl large enough to hold 4 cups of whipped cream. Chill the beaters.
Combine the gelatin and water. Let sit for 5 minutes. Place over low heat and stir until the gelatine is completely dissolved (about 1 minute). Remove from heat and let cool.
Whip the heavy cream in the chilled bowl until it begins to thicken. Continue beating while slowly adding the sugar. Add the vanilla extract. While still beating, slowly add the gelatin. Whip until soft peaks form.
Imediately use to frost a cake, put into molds, or fill pastries. Place in the refrigerator to completely cool. The gelatin will set, stabilizing the whipped cream. When brought back to room temperature, it will not lose its volume or shape.
A word of caution, whipped cream is made from cream and needs to be kept relatively cool to avoid spoiling, just as do all dairy products.
I have used this topping succesfully and highly recomend it for cakes and pastries. It's good stuff.
Seeeeeya; Goodweed of the North