1. Line two baking sheets with parchment. Using a small ice cream scoop, portion 12 scoops of ice cream. Put 6 on each sheet. Cover with plastic wrap and freeze until firm, at least 6 hours or overnight.
2. Place sprinkles in a bowl. Combine chocolate and vegetable shortening in a heatproof bowl and set over a saucepan filled with about 1 inch of water. Place over low heat until water is just simmering (be sure bowl's bottom does not touch water). Cook, stirring often, until shortening and chocolate are melted and smooth, about 5 minutes. Remove bowl from pan and let stand until chocolate is just warm (not hot) to the touch.
3. Working quickly, scoop up 1 ball of ice cream with a fork; hold ball over bowl of chocolate and spoon chocolate over to coat, letting excess chocolate drip back into bowl. Hold coated ice cream ball over bowl of sprinkles and top ball with sprinkles. Use another fork to gently push coated ice cream ball back on baking sheet. Repeat with remaining ice cream balls. Freeze until ready to serve, at least 30 minutes.