Welcome to the Forum Jimidybone. I would say a collection of this type is important and should be kept together. There are several firms that specialise in buying collections, Colour Rail being one of them. Inspite of their name they also have B/W collections. Try following this link:
http://www.colourrail.com/Default.aspx
Collection of railway photos are important so do try to find a buyer and keep the colection together.
Best wishes,
John H-T.