Exile Machine in TX sells mags to Calif. in "rebuild kit" form broken down.
Some 10 rnd M1A mags here on pg. 2:
44Mag.com does sell M1A/M14 mags & floor plates (Checkmate brand), but they are out of stock like everyone else except for 5 rnd :
AND, here is a short FAQ on M14 mags. It has some critical info on mag body wall thickness specs and follower hardness - a very good read: