There are a number of Sigma lenses with OS in alpha-mount. I believe they discontinued the OS from a few (not lowering price), but left it on others. I have the Sigma 70-300 with OS and it works just fine with LA-EA2 and NEX.
I've never really been bothered by the loss of light from the LA-EA2 mirror, but perhaps I'm just not a discriminating enough user. To me, the NEX has such absolutely amazing high-ISO performance, it more than compensates. If anything, I might buy that as a more valid criticism of my A-77 SLT mirror, just not my LA-EA2.