The Garritan instruments are merely a variety of common instruments, they never claimed to be a complete selection of available instruments. If your needs are not met by these choices, then shop around. There's many different sample developers available. Orange Tree samples comes to mind as have several different guitars.

You will have to create custom HP preferences with these libraries.

https://www.orangetreesamples.com/products 

Thanks very much Jeffrey, I had not seen Orange Tree before so that is very interesting.  I should have explained one of the main reasons that I would prefer to see a greater choice of instruments in Garritan.  It would appear that the integration of Garritan with Finale is better than other libraries.  This isn't surprising of course, but it seems that the integration between Finale and (for example) Kontakt is not very good.  I have struggled with this for years - and both Acoustic Legends (which I already have) and Orange Tree work via Kontakt.  For this reason I'd prefer to see more instruments in Garritan, or at least find another library that integrates better with Finale.  As just one example of what I mean ... as far as I can see one can only create Key Switches, which I need for Guitar work, in Finale using Garritan.  I would love to be told that I'm wrong in that notion, but so far it has been a big struggle to integrate Kontakt-based libraries into Finale.  It sort of works, but the functionality seems limited? Am I wrong?

I completely understand your frustration with the limited guitar instruments in Finale, especially considering the diverse range of guitars you work with. It's surprising that the variety in Garritan Anthology doesn't cover a comprehensive set of guitar options.