I tried Googling specifically for Welch's frozen grape juice concentrate and only got two hits, both sold out.
I found my sweet wine recipe from 45 years ago. 1-12 oz can of concentrate, 4 cups of sugar, 1 tsp wine yeast, (I used bread yeast back in the day and it worked fine), and then water to fill a one gallon jug.
Since a can made 48 fl. oz., I guess 5 of the 48oz jars would do the trick for a 5 gallon batch. 28 days and siphon into secondary, 7 days later bottle or drink up.