One of the best aluminum magazines on the market is the Brownell's. They have a USGI contract to make these for the military.
They make these in 5, 10, 20, and 30 rounds, in standard gray or Coyote Brown, and with your choice of stainless steel or silicon springs.
Since the military do issue these, quality is first class and Brownell's has a No-BS lifetime guarantee.
Best is the price, which right now is $9.98 for a 30 round.