same-sized alternatives to F14T12 bulb
Nope, 8” is the wave of the future.
Nobody wants to make T12 LED retrofits because the extra diameter serves no useful purpose, makes packaging bulkier and could have fitment problems in fixtures made for T8.
As big a fan as I am of real fluorescent, I advise oddball fixtures like this simply be converted to LED with ballast-bypass &quot;tubes&quot;.   While real fluorescent  will  be supported in T8 for the foreseeable future, the odd sized tubes will be pricey.