To be clear; The chain is still available. That's a standard replacement part for a different application; Aftermarket HV058 Transmission Chain, .875" Wide (42 Links) (Rigid Chain) | eBay
The gears/sprockets are the unicorns.
That sounds right.this thread here says the GXP chain (which has superseeded the older 4t65e chains as a replacement ) is heat treated and stronger. GXP Chain