Only Irritrol manufactures the 205 valve. Does the existing valve work? The same valve, with a standard 24V solenoid, can still be found in common use. If the existing valve was still functioning, there are rain detectors rated for line voltage. Actually the usual mechanical detectors already contain a microswitch that's rated for line voltage. It's the extended hookup wire that is not rated for line voltage.
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Your cheapest reliable plan of action might be replacing the entire valve with a Lawn Genie valve, which is also made by Irritrol. It will closely resemble the professional version, known as the
2713APR, which is available on this website's online store. You have to cut and recouple the outlet pipe, before and after you unthread the original and thread on the replacement. A union fitting will come in very handy in reconnecting the outlet piping.