I could not find a recipe for blackberry frappy, but you will get the idea. If you do a web search for Raspberry Frappe you will get some information.
Here is the recipe for Blackberry Cordial as given in the old cook book "Common Sense in the Household." I don't know where you could buy blackberry, raspberry, or elderberry juice. Maybe you could boil a fruit mush in a little water and then strain. Discard the bag of spices after boiling. Best brandy means at least 100 proof.
At one time, 1950 to 1970, the Pogo comic strip was the most popular strip in the newspaper funny pages.
Here is a recipe for a Blackberry Frappe that I found recently. Kummel is a sweet, colorless liqueur flavored with caraway seed, cumin and fennel. I would leave it out and double the two other ingredients. A frappe is served in a small, stemmed glass as in the pictures above, and below.
Kummel Blackberry Frappe
1/2 Oz. - Kummel
2 Tsp. - Blackberry Brandy
1 Tsp. - Lemon Juice
Combine and stir. Strain over crushed ice.