Is it possilbe to but higher gears in a samurai transmission to improve highway speed and fuel economy and if it is where is best place to find the gears?

Nope.  Unless you want to cut them yourself....

The only variation on the transmission gearing is, I believe, between the pre-88.5 and the post 88.5 models and that involves 5th gear.

Actual info in on this site on the tech specs page (see menu bar at the top of the page).

Most folks perk up performance/economy with a combination of an engine rebuild, aftermarket carb swap (ZOR's MySide comes to mind) and aftermarket exhaust systems.

As mentioned, the 86-88 trannys had a .795 5th gear vs. the .865 5th gear of the 88.5-95 samurais.  The ratio change is good for about a 300 RPM drop at 60mph.
You could also run a little taller tire, to drop the RPMs a little more.  But you will also lose a little bit of driveability with bigger tires....little more sluggish to accelerate, little harder to maintain speed.

thanks for the info