OK on fist glance there is an issue with the charge (aka source) coil, this is to charge the ignition capacitor in the CDI not the battery.
Check and double check the connections near the magneto. has the wire come off the plug or socket, any corrosion etc. Unplug it and test from the connection on the mag side and an engine case screw, is it the same?...confirming a coil issue. I cant help thinking this is a connection issue, you dont just 'go on holiday' come back and find your coil went kaput
If it still tests bad, pull off the flywheel and give it a viual inspection for now.
Electrex world will supply you one and your bike will no doubt be up and running cheaply but it will not likely fall within the quoted spec of 420 Ohms, I have one of theirs fitted at the moment and it measures 381 Ohms . A yamaha one will be expensive unless you get lucky on ebay ...which is doubtful. I just bought myself one from the states. All things considered if it were me I would go for the Electrex world one.
Other concern is the black/white, disconnect it at the CDI when testing for spark in the short term until you find the reason for the apparent path to earth.