The CWBP is pretty old. If it aint mapped by now consider it free to map. Maps 2 & 3 have a thread thats been abandoned. Map 5 has an abandoned thread and Map 27 was the one GP was taking on does not have a thread so you can create one in the same style - "[Region 1][Map 27] BlahBlahLand" and start mapping.
If you want the relief / height maps or a template for that map tile then just shout in that new thread. The others have got them already. The only thing we ask is that it lines up with neighbors and that the maps are all creative commons share alike because a) the base map is in that style and b) it guarantees that its free to use and share.