In the 1990's I bought a leather holster that was marketed for the webley tempest . it fitted the HW45 great.
One like this
https://www.timdysonairguns.co.uk/wp...3/DSC02904.jpg
https://www.timdysonairguns.co.uk/wp...3/DSC02913.jpg
Edit found one for sale with a HW45 https://s3-eu-west-1.amazonaws.com/l...30_540x360.jpg
Not a shoulder one but could be modded to make one.
Pretty sure I tried one made for a .44 magnum but it did not work right