In looking at the origin of this rose the only thing we can be certain about is that it was named after Charles de Mills, Director of the East India Company in the late 1780s.
It appears that nothing concrete has been discovered regarding its origin. From our reading it appears likely that ‘ Charles de Mills’ was once known by a different name which has become blurred by generations of distortion. The thought it that this rose may have originated in Germany named ‘Charles Wills’ and was subsequently renamed ‘Charles de Mills’ upon arrival in France.
Not an off the shelf item, it would need to be ordered from your local garden centre.