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There are online sites below (and others out there too) that cross reference, but some are incomplete and the sites don’t always agree with each other. The number in the middle of NGKs is the heat range and the higher the number, the colder the plug. If 2nd character is the letter R, it’s a resistor plug. If 2nd letter is a Z, it’s what NGK calls an "Inductive resistor" which is a small coil that blocks radio interference like resistor plugs do, but without soaking up as much energy as resistor plugs. If there is a dash number on the end, like -10, it is made to have a .010 larger gap than the same plug with no dash number.
Good Luck!
Dave
http://www.sparkplug-crossreference.com/
http://progreengrass.com/spark-plug-cross-reference-chart/
http://www.sparkplugcrossreference.co.uk/search/
This NGK site has a cross-reference function too: