This probably sounds like a stupid question, but how do you get scales and diamonds?

Scales- go to hatchery and click "nurture sylesties" then click and nurture the eggs and hatchlings of others.
Diamonds- go to diamond shop and buy them with Real Money or buy them in currency exchange for gold

You'll have to nurture correctly to get scales.

For eggs:
cool - warm
warm - cool
restless - turn
dull - polish

For hatchlings:
weak - work out
derpy - read
hungry - offer food
restless - play
slow - race

Thank you both ^-^