While the forum serves to exchange knowledge freely, we cannot encourage the home conversion of semi-automatic firearms to full auto.
Such tasks are best left to licensed Class III gunsmiths who have the training, experience and the skills to perform the conversion. Unsafe conversions can result in permanent damage to the firearm and serious, if not fatal injuries to the shooter and bystanders. Witness the unintended consequences arising from unauthorized alterations of a Sig P220 which was reported earlier.
As Mykl suggest, your safest route would be to contact a Class III gunsmith who can supply you with the parts, install them, and assist you with the necessary paperwork for lawful possession of the firearm.
By the way, the M14 in full auto isn't very controllable and the Army locked the selector switch on the rifles issued to the troops to semiautomatic only. Even the heavier bipod equipped M14A1 intended as a SAW wasn't very successful.