How to get the immature balance of an account? I have run bitcoind and have several accounts. How do I get the immature balance of one account using RPC calls (if possible) ?
Using the listtransactions command, you can see your immature coinbase transactions listed with category immature.

listtransactions appears to include both spent and unspent transactions in general, but since immature coins cannot be spent, that shouldn't be a problem.

Since accounts are now deprecated, you can get the immature balance for the entire wallet with getwalletinfo; look at the immature field.

Note that getbalance does not include immature coins.