Ordnance Survey Landranger
If you want to use the classic 1:50,000 Ordnance Survey Landranger there are two sheets which cover the whole route. The route of the Allerdale Ramble is no longer marked on these maps although it was until 2010 so if you have an older copy you may find it there.
Ordnance Survey Explorer
For walking we prefer the 1:25,000 Ordnance Survey Explorer range as it gives a lot more detail on the ground including field boundaries, which you don't get on the Landrangers and are very useful when you're trying to find footpath. Again the Cumbria Way is no longer marked on these maps.