When we need something, we run to the corner store store, or worse, the mall. When we some thing for the boat, we run to the chandlery, West Marine most probably. What we need is on the shelf. Seldom do we give a thought to making simple tools, though isn't that capability what made us human? Back in the day, for a workman to make his own personal tools was central to the craft. What sailmaker bought his fids from a store? Seam rubbers and wooden fids were crafted as needed, to the individual taste and hand of the worker. Some made fids with a handle or a turk's head worked in a turned grove; this probably worked best for large course hemp lines, but on a small boat with synthetic line, needs have changed. Even my wooden fids are smooth, so that they can pass through one line, towing another. The point is they were made by me to work best for me.
My finishing bench is of my own creation, fits nicely next to my favorite chair, always holding what I need near at hand (I have another sewing kit on the boat). It is a bit smaller than old-time benches, better suiting the size of my projects.
My wooden fids were turned from scrap hardwood dowel in a drill press (I have a lathe, but the drill press is handier for this) and have been worn smooth. There is a hole in the butt to accept a towed line, when that is required.They took perhaps 15 minutes to make, and I enjoyed the process.
My hollow fids are discarded knitting needles. Ask your wife or daughter--I'm they have a few mismatched needles about--or go to a thrift store. Cut to length, smooth the outside edge with a file or sandpaper, and clean the inside edge with a hand held drill bit. I seriously doubt the commercial hollow fids were purpose built, as the volumes are far too low--they are re-puposed knitting needle blanks, I'm sure of it.