I've actually just read another article written by licensed repairmen who all said they use specific ceramic fuses of a very high rating and they are not available at the usual sources (radio shack, tandy, Dick Smith etc) but sourced via the manufacturer.
More importantly, they all said it was an extremely dangerous job for the untrained as, even with all power off, they can hold enough current to kill you and there's a specific way to 'bleed' them first.
Most also said that usually it's a sign the magnatron is on it's way out (which is why they blow) and they are an extremely expensive item.
I'd look into it a bit further before just ripping it out (maybe ask a service centre for a price which should tell you how easy or otherwise the job is).
Trifstar
August 2011