A British writer friend of mine recently made the comment that she had little idea where and when writers' conferences took place. I was sure that there must be a way to track these events down so from a trawl on the internet, I came up with the following.
Winchester Writers' Conference
Milford Writers' Conference
Edinburgh Wold Writers' Conference
Get Writing Conference
Swanwick Writers' Conference
Southern Writers' Conference
Northern Writers Workshop, York
Williamette Writers Conference
Wikipedia has a list of writers' conferences too. Have a look.
In the UK, you can also find news of writers conferences on the British Council website.
Other places to look are writing magazines, online and on noticeboards at libraries.
Finally, you can read about the benefits of attending a writers' conference here.