I have Hogue 1911 grips on my HW45 too and I also bought them from Midway UK - part no 563401. I bought a set of Pachmayr grips at the same time as the postage was the same for both to see which I preferred. The Hogues suited my small paws better so I sold the Pachmayrs here.
The HW45 was created because Dr Beeman asked Weihrauch to make a spring pistol as close to the 1911 as possible.
For those with HW40s, there's a Hogue slip-on grip, part no 662386, that greatly improves the handling. Not as easy to install as the HW45 grips but well worth the effort.