I bought an SAR-3 when they first started coming into the country. At that time, there weren't any 5.56 mags to be found. I modified three 5.45 mags to work in my gun and that involved making room for the shoulder and filing a slight angle into the feed lips. Two of them ended up working great, while the third would kick rounds out of the magazine, and the ejection port, when bolt was recoiling, causing the bolt to fall on an empty chamber. In any case, it was horribly painstaking and had mixed results. I wouldn't do it again.
K-VAR has some of the Bulgarian waffle pattern ones in stock.
http://www.k-var.com/shop/5.56x45mm-.223-Caliber/
...They are expensive, but are the best you will find short of Weigers.
...And if you must have Weigers, it looks like Apex has them in stock for a little more money than the Bulgy waffles.
https://www.apexgunparts.com/magazines/ak-wasr-3-sar-3-wieger-30rd-magazine-steel-5-56-223-excellent.html
Good luck with your build!