score:4
I don't see any problem at all at finding a cab at Navtlugi or wherever you want in Tbilisi. Just rise you hand on the road and any free car will stop near you.
And also I am sure that plenty of cabs reside on the Navtlugi station.
However, if you want to be super safe, you can call taxi by phone with following numbers:
2 717 717
291 14 14
2939 100
2535 535
2200 200
0322 10 50 50
2 201 201
2 30 88 88
2 377 877
2 939 939
247 77 44
293 91 00
291 14 14
274 74 74
2 27 26 26
551 999 244
571 999 244
230 03 01