What with the release of the intereactive map, I took the liberty of finding any and all unplayable factions and list them by region. I am missing about 13 of them, but I think I got most of them, and also they're porbably alot of spelling errors. :/
Britain:
1. Ebdani
2. Caledones
3. Brigantes
4. Demetae
5. Dumonii
6. Iceni(Playable)
Gaul or Gallic Tribes:
7. Namnetes
8. Carnutes
9. Artrebartes
10. Treverii
11. Aedui
12. Pictones
13. Volcae
14. Vivisci
15. Helvetii
16. Massilia
17. Nori
18. Raeti
19. Scordisci
20. Eravisci
21. Breuci
22. Boii
23. Averni(Playable)
Spain:
24. Cantabri
25. Galleaci
26. Arevaci
27. Edetani
28. Celtici
29. Lusitani
30. Turdetani
Germany:
31. Cimbri
32. Rugii
33. Gutones
34. Cherusci
35. Nervii
36. Sequani
37. Frisii
38. Lugii
39. Marcomanni
40. Seubi(Playable)
Italy:
41. Estruscan
42. Liguria
43. Syracuse
44. Insurbes
45. Rome(Playable)
Hellenistic/Greek
46. Knossos
47. Rhodos
48. Pergamon
49. Seleucid
50. Macedon(Playable)
51. Athens(Playable)
52. Egypt(Playable)
53. Sparta(Playable)
54. Eprius(Playable)
Africa:
55. Nova Carthago
56. Gaetuli
57. Libue
58. Garamantia
59. Nasamones
60. Cyrenica
61. Meroe
98. Axum
99. Belmmyes
62. Carthage(Playable)
Steppes:
63. Aestii
64. Budini
65. Anartes
66. Catiaroi
67. Cimmeria
68. Siraces
69. Thyssagetae
70. Scythia
71. Massagetae
72. Dahae
73. Khorasmii
Eastern:
74. Bityhnia
75. Nabatea
76. Himyar
77. Saba
78. Mascat
79. Parthava
80. Sardes
81. Cappodocia
82. Cyprus
83. Qidri
84. Media
85. Armenia
86. Media Atropatene
87. Baktria
88. Persia
89. Arachosia
90. Dragiana
91. Sagartia
92. Aria
93. Colchis
94. Kartili
95. Ardhan
96. Gerrhea
97. Ma in
100. Pontus(Playable)
101. Parthia(Playable)
Misc.
102. Beiphi
103. Getae
104. Bastarne.