No suprise a governor spring broke: there are heavy weights attached to them, and if the parcel is mistreated, they're the first thing to go. I suggest you also try to write to user
soundgen on this forum, as in some cases he has more spare parts than he advertises, and is very knowledgeable and helpful in any case. Ask him about the soundbox as well, you never know. The Crescendo Junior Soundbox are not "rare" in strict terms, thousands and thousands were produced, but obviously they tend to stick to the gramophone to which they belong, so find a spare one might require time and weeks of digging on ebay.
This one apparently remained unsold, it obviously lacks the screw, but if another screw came with the gramophone it may be worth dropping a pair of lines to the seller:
https://www.ebay.it/itm/THE-CRESCENDO-J ... Sw9BBf0QDB