Looking at the parts fiche (its in the documents section of the home page)
http://www.400greybike.com/files/FZRRRSP.pdf
The mirror brace/stay appears to be the same for all models; 3TJ-2831W-00
It also appears to be exceedingly rare ; not surprising as it will be the first part damaged in an accident.
No searches on the web appear to reveal any relevant info or sources.
Previous comments on this forum advise replacement with a new part rather than repair when the topic has been
broached in the past, so it must have been available at one point.
Armed with your frame number and the part number, a call to a Yamaha dealer may yield results; they have access
to stocks held worldwide.
A used or new old stock part may surface in time on the usual auction sites.
It is always worth asking a seller if the part is available when a "breaking bike" style ad. has been placed.
A good fabricator could make a replacement using sections from the original if it has not been discarded.
Race glass or aftermarket fairing manufacturers will not have the bracket; they specialise in plastic/fibreglass
products and expect the buyer to fit the product using the original makers brackets.( usually with quite a bit of
fettling/finishing)
The mounting of mirrors is not difficult providing the stay is in place.
Without the stay the extra weight/vibration and flexing will undoubtedly damage any fairing when mirrors are added.
Keep up with your searching; you may get a result from your ad. in the wanted section.
Well done on trying to get the bike back somewhere near to its original condition.