Sell them and buy extra normal ones.
If absolutely need be, if they're like the ones when I had a Saiga, it's a matter of five minutes with a dremel. Measure normal mags, transfer the measurements to the Saiga mags, remove what's outside the measurements.
The only differences in my case were that Saiga mags had a thinner rear lug and wouldn't fit with a feed ramp installed in the gun. Regular AK mags worked just fine in my Saiga after a gentle touch with a file at the latch, but it was just a matter of removing about 1/8" out of the front of the mags to let them fit past the ramp. I had a mill, a dremel would work.
With the price on them nowadays? Sell them and buy twice as many imported steel ones.