This might be a very basic question and might have been discussed, but I want to make sure I understand it right and hence stating along with problem
I am trying to use bouncycastle for my operation if that helps.
Unfortunately the bouncycastle API does not provide this functionality out of the box.
You will need some extra coding to achieve it through the bouncy castle class PGPPublicKeyRingCollection.
You can also check this example from a commercial BC wrapper that provides such feature: http://www.didisoft.com/java-openpgp/examples/import-keys/