The 5.56 AK's don't seem to be super popular, I think in part due to the lack of there ever being a standardized design. Bulgarian, Polish, Russian, Romanian, Yugo, and the Chinese all had their own take on how to build a 5.56 Kalashnokov. I've had my SLR-106FR since 2008 and it might be my favorite AK. It's pretty rough on brass so I mainly shoot steel cased stuff through it, but it eats everything just the same. I bought a good sized pile of waffle mags for it initially so I wouldn't have to worry if they went up in price or became hard to get.
I think the prices on 5.45 ammo and AK-74 for the better part of the last decade is another reason the 5.56 isn't as popular. Crates of Russian or Bulgarian surplus 7N6 ammo for $210. 12 packs of surplus mags from ORF for $36 if I remember correctly. Black, brown, saddle tan, firebrick red, plum, true black. Collect 'em all! If the prices had been what they are today, I think 5.56 would have been a more attractive option for people who wanted something other than 7.62.