Many of the Spanish guns have a ramrod spring located inside the stock. However with those guns, there's an opening in the stock between the barrel channel and ramrod hole, which allows the spring to swing upward and contact the bottom of the barrel which in turn places enough pressure on the ramrod to hold it in place.
The ramrod spring is designed to pivot and is not stationary.
See the diagram:
It may be possible to simply wrap a piece of tape around the ramrod to tighten its fit within the stock.
IIRC a more traditional method is to melt a small bead of wax or beeswax inside of the opening of the ramrod hole which should help to wedge the ramrod in place using a friction fit. When the wax wears out then add some more.