You might want to try the r/starbucks subreddit, as this one is intended for baristas.
But the short answer is, to make an actual frappucino, you'll need to use xanthan gum to stabilize the beverage, otherwise you'll end up with blended coffee ice milk. At home, you're better off making a milkshake with some coffee ice cream from the grocery store.

Eh maybe a vita instant iced coffee could replace what we use in frappucinos. We also use whole milk and ice with whatever flavors/ ingredients go in said frappucino. Hardest part to replicate would be our base which helps mix everything and not make it super stuck. You might be able to buy one from an actual starbucks, but not 100% sure.