You can get screw slot files from Brownell's, Montezuma, IA. I believe tey're European imports. For other files, I use MSC but be careful about brand names (manufacturers). I prefer Nicholson but the last batch of Nicholsons were labeled "Made in Brazil"; they seem to work as well as the older ones made in the USA. Grobets, from Sweden, I think, have given me good service.
Others here can perhaps give more recomendations.
Dave Dolliver