LM317 only works on DC.
One way to get the AC voltage you want is to add a wire wound resistor. The voltage you get will not be accurate and it will vary according to the current you draw.
But, for instance, if you are drawing 1amp, put a 3R3 5watt wire wound resistor in one line and measure the voltage.
If it is too low, put a 10R across the 3R3.
Alternatively you can put a wire wound pot (called a rheostat) in one line and adjust the voltage. (These are expensive and you will need a 10 watt version.)
The other method is to put a number of 1 ohm wire wound resistors (5watt each) in series and use a clip to tap off the voltage you need.