A local hardware store had spare parts for old Mags and in the boxes I saw some spanners. Basically PVC with a couple pins mounted in the end. I was going to buy one for C Mags but they wanted $7 or $8, IIRC. Seeing as how I had no immediate need, I passed on it. Seemed like a lot of money for the construction.
If you'd like, let me know what size you need and I'll check next time I go by. Figure cost plus shipping, maybe $10. Be warned, it might take me a week or two to get around to it.
Another option if you have acess to a drill press and lathe, is to drill holes in the proper size PVC tube, insert pins and turn down to size need to fit battery tube.