I think I found a consistent supply of peanut butter, and I'm so happy if this works out!
(See this post for a description of the ordeal of hunting for peanut butter in Astana)
Across from Keruen mall (near the Beiterek tower) is a small store called Fine Foods. It sells expensive European products such as bread, jellies, and fresh fish imported from Europe. A couple times last year I bought peanut butter there--1800 tenge (over 11$) for just 500 grams (a normal-sized jar) of Dutch peanut butter.
Since returning in early August, I haven't found peanut butter at any of the usual places, or at Metro, which only recently seemed to acquire peanut butter, and so I stopped by Fine Foods yesterday. I couldn't find peanut butter, so I asked a worker, who had never heard of peanut butter but was convinced they had what I was looking for, and showed me something like Nutella as well as different kinds of butter.
A German guy (perhaps the owner?) came and he knew exactly what I was looking for and said it was in stock. I gave them my name and number and they said they'd call when they had it in the store. Also, he seemed to imply that I could order peanut butter from them and they would get it, just for me.
A few hours later they called to say they had peanut butter. I haven't had time yet to go pick it up. But I'm excited. It's expensive, but if I can order it, then that means I'll always be able to get it. Yay!