Naff,
I have recently seen Villers engines on e-bay, look on the 'rotovators' or into 'small engines' and see whats there, there is also a link to a company on e-bay that are doing brand new engines of 5hp for £80-£90 they are 'Robinsons based in Hainault, Essex(0208-559-6000) obviously these are Chino imports but are based on Honda/Briggs&Stratton engines and might suit your purpose, other than that try 'Tillerparts' down in Kent and contact Chester Hudson. :)