There are tourist offices in the following cities of Crete. The information that you get is in general pretty limited.
Chania Information Office Kriari 40 - Megaro Pantheon - 73100 Chania Tel : 2821092943, 92624 Fax : 2821092624
Rethymnon Tourist Office Eleftheriou Venizelou Paralia Rethymnou - 74100 Rethymno Tel :2831029148 Fax : 2831056350
Tourism directorate of the island of Crete Xanthoudidou 1 - 71202 Heraklion Tel : 2810228225, 228203 Fax : 2810226020
Crete information office Marina Agiou Nikolaou, - 72100 Agios Nikolaos Tel :2841082384, 5, 82386 Fax :2841082386
There is also The Official website of the Greek Tourism Organisation which can be of (limited) use.