Where can I get a map showing the location of, for example, my great grandfather's family croft?

Most local and family history societies hold all large scale maps covering their catchment area. We suggest, however, that you arrange to get the map(s) in advance of your visit. The 1:10560 (6 inches to 1 mile) Ordnance Survey (OS) 1847 series is, perhaps, the most appropriate, although much of Scotland was also mapped at 1:500 (25 inches to 1 mile).
These can all be ordered from the Map Library at the National Library of Scotland at www.nls.uk/maps.  Large scale (1:500) OS maps of 62 Scottish towns can be viewed online at the above website for free.