None for now, all you can do is stay updated by using the bounties section in altcoin discussion thread and you will see when new bounty get added, honestly most new bounties are total waste of time but if you can do research on them you will know which one is worth promoting
the section altcoin service annoucement are i think the one that will first announce if there will be a bounty that will go live and then you will see it being released on the altcoin bounty section .
and how can you say that most of the new bounties are only a waste of time ? its known that bounties were now full of scam but even older bounty sometimes turned into scam while some new bounties are going to end succefully . not all are the same .