Hi, welcome to the Makarov Forum. Single stack Mak mags are a real good example of supply and demand. The price has gone North of $25, in general, but can be had. Sometimes the "deal" can be found. I'd start with Slim Tim's Makarov Trader (right here on Gunboard's topic menu), Ebay and your browser's search engine.
There are still a lot of surplus parts spread out over a multitude of retail parts houses...again use your browser. Really too many to list, but at least you can "shop" and compare price points (most parts are generic and interchangeable between all Makarov PM variants). Again, if it's a specific part, I'd start with a WTB request on Slim Tim's Forum.
Hope this helps some.