only the chinese siminov variant, the sks model 'd' (also called the model 'm') accepts kalashnikov (ak-47) high capacity magazine.
the sks model d/m's were all sold long ago. there are very, very few left on the shelves of retailers that got stuck with them. you can pick up a good, clean used one off of auctionarms.com, gunsamerica.com or gunbroker.com for $300-400.
in my expirience, a siminov is only slightly more accurate than a 7.62 x 39 kalashnikov. both are limited by ammunition availability. the kalashnikov, equipped with an optic mounting rail, offers a better platform for telescopic sight usage. the siminov offers a longer sight radius.
other sks's accept the factory/military 20 round fixed box magazine and the semi-detachable 30 round aftermarket magazines.
some of these work fine, other are no better than paperweights.