ethereum this you can get in several ways. First, you can get by swapping the coins you have with ethereum in the exchanger. The second way, is to follow a bounty which rewards in the form of the ethereum. And the third way is by mining ethereum.
well? i think that it is better to go the first or the third way as i would not trust bounty campaigns it is too hard to choose the right one
Though you are correct regarding on finding the right project to do some bounty and earned ETH but still that's the common ways to collect some ETH
after exchanging the coins you received, converting bounty coins to make some ETH mining also can be a good source but its needed a lots of investment,
as difficulty mining this coin is really high now.