Are you sure about this statement?
Yup.
Where I live there are many phone repair shops run by mostly people from a foreign background living a marginal life who may be willing to take a chance, but even they favor repairs on common equipment like iPhones. Most won't have been near a FireWire interface or a film scanner. Actual computer repair places tend to keep repairs limited to swapping out components in desktops and laptops, and will rarely solder anything. Been there, done that for a decade or so - and yes, that was in an era when we occasionally took a fried main board to the importer and someone would manually solder a new chipset onto it. But those were the 1990s, and even those madmen only worked on stuff for which they had the full schematics and spare parts, not to mention it was still viable to have someone with an EE degree working in a place like that back then (not in an actual computer repair shop of course; virtually nobody knows the first thing about electronics there, not back then and sure as heck not today).
The FireWire interface in a scanner is not some kind of neatly delimited module with a 4-pin connector you can solder off and replace with a store-bought part. It's a bunch of chips and passive components strewn across a larger pcb with several other functions and your have to start by troubleshooting it with a scope and perhaps a logic analyzer to figure out where the problem originates and then pray it's a component you can still obtain.
I think you're underestimating the complexity of something that sounds easy enough; "oh, we'll just swap out the FireWire interface". There's a lot hiding behind an innocuous sentence like that.
You might be able to find a hobbyist who's willing to spend some time on this. I'm involved in something similar revolving around a Nikon scanner for a forum member here. There's no guarantee whatsoever it'll ever work and it sure as hell wouldn't be an economically viable enterprise to do repairs like these given the time they tend cost.
Don't get me wrong; I'd love to be proven wrong because that would mean you'd get your scanner fixed quick and easy and at low cost - provided its defective in the first place that is, because your observation that neither port works can still just as well mean you have another issue like a driver problem or an issue with the FireWire interface on your computer.