Attainable diamonds regularly found here (2,3,5)
I believe the answer is:
on the cards
'attainable' is the definition.
(something on the cards is viable or attainable)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for on the cards that I've seen before include "Where pips are" , "place for 6 19 [SEASONALMESSAGES]" , "Likely to happen" , "expected" , "Greetings may be" .)