How can I get more amps from a voltage regulator?
TI's datasheet shows to ways to increase the current output of a 317. The first one is basically what you're suggesting:



Notice the 0.2 Ohm resistors at each output. These allow for differences in the reference voltage between the 317 chips.

The second one uses external transistors instead of paralleling 317's:



This concept can also be done with a single external transistor as shown here: