There is a seller on eBay that seems to have access to FH-M10/SH-M10 holders. Do a search...
He's from Russia (yeah, I know!), but I ordered the holders a month ago anyway. I wanted an extra set as I want to make a glass holder, but didn't want to risk ruining my original holders. To be honest, I was expecting this to be a scam, but I actually got the item as described. Shipping took 3 weeks, seller provided the tracking number a day after my payment. I left positive feedback (my eBay username is 'boarchi'). I saw today that he's got another set for sale.
Slide film holder is identical to my original SM-M10 holder, FH-M10 is a bit different. The cross bars between frames are like those on FH-M20 holders (for Minolta 5400 v2). But both holders work OK in my scanner. New negative holder even allows for scanning of a bit larger area of a frame.
I have no connection to the seller and this was the first time I've dealt with him. I'm not responsible if your transaction doesn't go as smoothly as mine...