Those sockets are actually your basic Amphenol blue plug and socket. The 50-pin version of these you can find on the end of most any OLD multi-line telephone (at least in the USA). Look in most any business closet and you'll find a few unused ones you can borrow.
The 37-pin variety is on the end of every older PC printer cable.
You need the 24-pin variety. These are harder to find, but can be found on both sides of the pond by googling "24 pin centronics connector" or similar keywords.
In a real pinch, you can take a hacksaw to your telephone or printer connector, cutting out the extra center section, and leave SIX of the gold-plated pins on each side. Crude but doable. If you're really clever, make the cut with a zig-zag in the middle so the two end pieces interlock a bit, giving a bit more rigidity.