WHERE TO GET MAPS
If you are looking for paper trekking maps, the best place to get some is Geoland store in Tbilisi. It offers maps of most of hiking destinations (sadly, Samegrelo is still missing). Shop is open from 10 am till 6 pm, closed on weekends.
In Svaneti, you can get solid hiking maps for free at Mestia´s InfoCentre at the main square. Another good place is the souvenir shop at the Seti Square (behind the Koshki café), it sells hiking maps from several publishers (Geoland, Terraquest and so on).
There is also a small enterprise named Hiking maps of Tusheti which, as the name suggests, sells hiking maps of Tusheti. Maps can be bought at Tusheti tower guesthouse in Upper Omalo as well as in Kvemo Alvani village at the shop at the crossroads, from which depart the jeeps towards Tusheti.
If you want to use smartphone for navigation, you can pick from a large number of hiking apps. So far, I wrote a detailed how to setup hiking maps for Georgia walkthrough for the Locus map app. In the future, I would like to describe a few more.
If you want to do some planning via desktop, probably the best hiking maps of Georgia available online were made by Geoland. They used to be found at the address http://mygeorgia.ge/geotrails. Sadly, the link doesn´t work more often than it does. A solid alternative is for example http://mapy.cz.
If you are for some reason interested in original Soviet military maps, those are accesible too. However, for a Westerner they can be quite cryptic as they use Cyrillic script. Maps can be accessed here.
Russian mountain enthusiast Mikhail Golubev took these slices and created from them huge map of whole Southern Caucasus. It can be downloaded here.
There is also an Android application containing all military maps mentioned above, it's name is "Soviet Military Maps". It can be installed for free from Google Play.