You never know when the opportunity will present itself! Bring it along! If it is a family owned B&B you could tell them of your hobby before hand, and ask them if they know of any places that you could hit. Who knows, they may let you detect on their property. It is hard to find private property to hunt on while traveling, not know anybody. You could always google map the standard locations such as parks and tot lots from each of your B&B's, however you are posting in the Relic Section so perhaps parks and tot lots aren't your cup of tea. Depending on where you are staying, I bet there are some farm fields near some old roads. Hopefully the owners of the B&B can hook you up with some contacts.
Jai