The absolute best aftermarket 10/22 mag IME is the Tactical Innovations.
They are in stock.
They start at 39.99 for polymer and go up to 99 for machined aluminum with replaceable steel feed lips.
http://www.tacticalinc.com/rim...e-mags-c-97_152.html
The machined aluminum ones are truly as close to indestructible as any mag could be. Before this, they were $69.99, now back to their regular price of 99. Actually worth it even at that price.
I have three of them and they are very very nice, and I am very very happy with them.