It's not just moulds, it's all the specialist machinery and jigs for each and every little piece that needs to be manufactured. Just try making multiples of a simple bracket, building the required jig can take longer and cost more than the actual product.Even if the moulds would still be existing, it would be a huge task to actually machine the parts out of the castings. As long as the drawings are still available not all is lost. However, in any case somebody would have to go the all the way to put them on CAD as without that nowadays it's virtually impossible to do any machining.
The moulds for the castings would not be too difficult to reproduce with today's tech and machinery.
In the end it's all a question of scale whether somebody would be willing to do this. I believe this was the basis for Aprilia or whoever to just scrap it.
CNC may be the answer for final machining, but even there, special jigs are required to hold everything in place on the machine. It's not as simple as clamping a casting in the milling machine vise, and, hey, presto, 10 minutes later, here's your new primary cover...
Things were simpler in the 1920-30s where "manufacturers" could order 95% of the stuff they required from outside suppliers. Major part of assembly was slapping the own brand name on the tank...
piet