Hi
Bournemouth is really popular for Hen night's and you should be able to get a good rate in October, although some hotels are a bit funny about taking group bookings for young man/females. There are loads of hotels on West Cliff Road which is really central to town. If you call the clubs before hand and let them know your a hen night party you might get a special deal and extra attention. Try Tokoy's, Elements, K Bar.
Hope you have a graet time, wherever and whatever you do!!