Try Electrolux (Sales 0870 0604 118).
They use a Washer Extractor and a Tumble dryer in our ITU to wash Nimbus 2/3 mattress covers. You will need to speak to them to get the exact specifications, (I have the spec's somewhere, but can't put my hands on them at the moment). They do the job for our ITU though.
Just be careful how often they are washed as it reduces the lifetime of the cover. I think the model numbers are W455H, T4130/C but I could be wrong. Hope this helps.