It took a bit of hunting on the internet, but I found photos which let me establish the general dimensions of the Raffin spool ends.  The details provided here may only work well in the USA because pipe and tube sizes vary between countries, but the design might be modified to use available metric sizes.

I used nominal 3/8 inch OD plastic tube sold as sink and water closet (American "toilet") water supply lines. This forms an inner shaft which I cut to a length of 160 mm. I heated one end with an electric heat gun (a hair dryer probably would work as well) and forced a short hex screwdriver bit into the hole. When it cooled it formed a hex recess which is a tight fit on the bit. It matches well with the gear rewind drive described in another "hint" because the same size hex bit is used for the shaft.

The center of the spool on which the roll winds is made from a 141 mm length of nominal 1/2 inch "Schedule 40" plastic water pipe. The outer diameter of this pipe is actually about 7/8 inch (21.5 mm). The inner diameter of this pipe is actually about 5/8 inch (15.5 mm).  I made wooden spacers by drilling a 3/8 inch hole in a short piece of 5/8 inch wooden dowel.  The photo shows how the spacer aligns the two pieces of plastic plumbing. If drilling the hole is too much of a challenge, paper and PVA glue could be wound about the inner tube until a sufficient diameter is reached.

The spool ends are made from Pocket CD-R disks which have an 80 mm outer diameter. I used a taper reamer to enlarge the hole slightly to 5/8 inch to fit over the spacer. This sounds expensive, but I have found these available for as little as $0.25 (about 15 pence) in some places, and readily available for less than $0.50 each in bulk spindle packages.

"Super Glue" was used to assemble the parts.  The photo below shows two of the spools, one with some of the greatest 20-note music available, the other waiting for my next shipment from Mel.