According to MMC the Super 3 front tyres are a unique size and currently only manufactured for them by Avon. They are available through Morgan dealers and cost about £210 per tyre in the UK.
Morgan will obviously have to keep the tyres available through the production run of the Super 3 which, based on recent history, is likely to be 5 -8 years.
It's pretty likely an alternative will be found during the life of the Super 3 or, worst case scenario, retrofitting different front wheels which have tyres available will always be an option.