Does the CA SAR Offizier M41 use standard G3 mags?
 

And if so, does it work well with TM high caps? I can't seem to find any Classic Army magazines specifically labeled for the M41.

Yes to both. STAR realcaps need a bit of filing to fit the receiver but it's easy enough to do with a pocket knife. CA makes both lowcaps and hicaps and are likely considerably cheaper than TM.