How to Add KFF/Accounting Flex Fields to a custom form in R12

we are  trying to develop a new custom Form in R12.2 and trying to add the Accounting Flexfields column for the user to select from a dropdown list. i tried invoking the the below procedure in the triggers but i don't see any output in the LOV or when i click on the Drop down list it doesn't show any values. when i checked if the 'FND_KEY_FLEX' package in available in DB , i don't see that package under all_objects. please let me know if i have to use a different package/API

FND_KEY_FLEX.DEFINE(

      BLOCK=>'custom_block',