I believe all of these are only used in writing Sanskrit in Kannada script. ಌ is the equivalent of Devanagari ऌ and Telugu ఌ, which is rare in Sanskrit, and unused in the modern languages. (Though the derived vocabulary is still there. For example: संकॢप्त > ಸಂಕಲ್ಪಿತ, సంకల్పిత, संकल्पित .)
According to this thread:
[ ೡ / ॡ / ౡ ] does not exist. It does not exist in any word anywhere in Sanskrit. At all. It is there purely for orthographical completeness, to complete the pattern.
You can Google "ಕೢಪ" to see ಌ used in Kannada script - but all of the results are Sanskrit. The same is true in Telugu.
The two ardhavisargas are also used only in Sanskrit, when a visarga comes before /k/ or /p/ or their aspirated versions.
They are all included in the Unicode block for Kannada script because this script is used for writing Sanskrit as well as Kannada.