In a [related thread](https://meta.mathoverflow.net/questions/2946/does-mo-have-an-official-twitter-account?noredirect=1&lq=1), it was pointed out that

> it seems that some users would consider having somewhere complete list of past bounties a good idea

While it does not do much for extending the bounty period (including very prominent advertising, and the reputation award for people who answer), it *is* possible to access the list of all bounties on the Stack Exchange Data Explorer (with some bugs for pre-migration bounties like [this one](https://mathoverflow.net/posts/959/revisions), which behave pretty wonkily anyway). The relevant query is this one:

### [Recent bounties](http://data.stackexchange.com/mathoverflow/query/510996/recent-bounties) on Stack Exchange Data Explorer