2 more suggestions, untried yet by me
1) solarisation; ie cover ground with transparent plastic a week or two before planting and if weather warm enough, bakes the clubroot spores.
Found this out by googling around- sounds worth a try
2)there is a product called armillatox which is sold as a patio cleaner etc but used also to be used for clubroot control, but since, the manufacturers say, it's too expensive to put through the required safety testing as per recent safety regulations, it can no longer be advertised for this purpose.
Their current leaflet says "reduces the severity of clubroot by drenching the soil or dibberholes with armillatox diluted with 100 parts water etc etc"
I intend to try it his year
hope this may be helpful