I totally forgot to post some pics of the velvet pouches I bought last year around Christmas. They finally arrived almost 2 months later. (thanks slow shipping eBay sellers) Anyway, so far they have fit all my compact Aiwa and Sony walkways perfectly, and even did so with the additional AA packs attached. I like these pouches better than the drawstring versions I've seen posted here before, because these are thicker, and have a simple loop/bead closure system. Not bad for $1 each (that was the price I paid at the time). I picked up 4 of them, but I should of bough a few more. I bought two with a secondary pocket on the outside, and two without.
I'd post an eBay link to them, but when an eBay seller runs out of stock, they ussually relist them under a new listing/link. Anyway, if you do a search for "velvet pouch" on eBay you'll be able to find many different sellers (many colours too).
There are many eBay sellers (about 250 of them right now). Some have the cheaper drawstring version, while others have the nicer, thicker ones (like the two shown in the pics I posted). To find them, I just did a search for "velvet phone pouch" and a bunch showed up. They start at $1.65 Canadian (around $1.25 US). As for the size, I don't have a tape measure handy, but it fits the Sony WM-FX822 nicely (as seen above), and would likely fit any other cassette player that is similar in LxWxH. I liked that fact that the AA battery pack also fits in the pouch while still attached to the player. Anyway, as mentioned, these bags are marketed as phone pouches. An iPhone 6S with slim case (which is similar in LxW as the FX-822, but only half the thickness of the Sony) fits just as well with plenty of room to spare on the sides and a bit on the end. Due to the pouch's overall size they can be used for a variety of things besides cell phones. The nice thing about using them for cassette players, is that even though the pouch is wider than the Sony in the pic, the Sony's thickness pulls in the sides of the pouch a little bit to make it fit more snugly around the case without putting undue pressure on any the buttons (Play, RR, FF, etc). They also come in a variety of colours, though some eBay sellers may not have all of them in stock. I'll be picking up a couple of dark gray ones next.