Actually, some older Norincos were factory modified to take 30 round AK magazines (had one I bought brand new in '90 and regret selling it). And others will handle 30 round duckbill magazines.
You will be looking at about $800+ for one if you can find it. I seen one on GunBroker the other day.
Also, click the link for the SKS boards in my sig line and you will find info on how to make ANY SKS accept AK mags. It's a risky mod to do as if it's messed up the SKS is officially a paperweight, but it is doable and has been done. You'd probably be better off finding an M or D model.
I looked into this with my SKS and just decided to go with a nice Tapco setup and became proficent in inserting mags quickly. It's not hard with practice. You can also use stripper clips with the Tapco mags, but it's harder to insert the rounds. Better off just switching mags.
Their pretty easy to identify by their mag well, and the fact that the mag in the mag well is a true ak mag. (come on you have to know what those look like right?) Saw one at a local shop a year ago and knew what it was right away. Be prepared to pay a bit more than a normal sks for one though.