Quick update...
Flex cable received, from a EBay seller representing www.ChinaPhoneAccessories.com. There is transparent glue on its back, while Nokia's original cable was attached by white adhesive. The cable itself is done well, but the glue layer is a bit bumpy, it seems to be too thick in one place. Everything works now, but the device will not be taken outdoors, yet: since two of the screws of the screen were destroyed, there is a small gap within the screen which would potentially allow sand and dirt to access and attack the insides, and it would be undesirable.
Updating the software, with hopes that even if the screen and the touchscreen stop working, N900 will still be usable. By the way, most of the blindly-made photographs turned out to be fine, even if they are not needed now: a long time has passed.