I'm the www.airguide.com.au
You can't buy those face plates new any more. If you find somebody who can do a nice duplicate face plate please let me know.
If you need a new mechanism, your speedos look very similar to the newest ones and I suspect the same mechanism will fit. i.e. diapraghm, adjuster etc. I can't promise though.
I can't help much with the old speedos as I've never had one apart. My first was a 1990 airguide which still goes great today - but it is the same 2025 model I have on my site.