if you can match the thread/diamter up to something else, there are loads of cheap CNC adjusters on eblag.something like this, but probably not this:https://www.ebay.co.uk/itm/CNC-Aluminum-Motorcycle-Preload-Adjusters-Fork-Bolts-Fit-for-Yamaha-YZF-R3-R25/123889478594?hash=item1cd8636bc2:g:6VoAAOSw-a9ekLgJWorth checking the american FZ sites to see if someone has done it and found a match.
Haven't your forks got these anyway? Every bike I've ever owned has had adjustable forks?
These adjusters will give you very little in real work feel and they'll will not be matched to the fork damping, you may as well add a stack of 2p on top of the spring. As for redound damping again the fork isn't fitted with this option as standard. The whole damping unit, would either need replacing or serious re-engineering to have it adjustable which wouldn't be worth cost, if you could get it done.
Take a look at Hargon. If you do just the front it will expose the rear and that often means you think doing the front has had no effect.