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These are the ultra-rare parts that you may have problems getting
You'll need two of these dual op amps. They are hard to get, but you can probably substitute a LM358 or any other rail-to-rail opamp that can go up to 30V input.
Ultra-rare. You're unlikely to ever find these unless they're pulled
A good substitute for the '662 if you current mirror the input. A little noisier though.
Very rare, hard to find.
A possible alternative is NTE44, which you can buy from Mouser
Somewhat rare, hard to find.
A possible alternative is NTE42, which you can buy from Mouser
You can buy these from Mouser, as they are still being manufactured!
Somewhat rare, hard to find.