Order some magazines directly from Ruger if you don't mind waiting a couple of months and paying retail:
http://shopruger.com/VS00510-SR40-SR...uctinfo/90350/
And jnichols is correct about cleaning out the striker channel. My SR9 had a lot of light strikes (misfires) in the first 100 rounds. Cleaned it out with some Gun Blast, so now it runs great.