Sorry - cannot recommend a Marina in Thessaloniki but flights with Olympic via Athens are cheapest or direct with BA - not much difference in price but easier!

FYI Thessaloniki Marina details

Marina Manager : Mr G. Patsioydis
Tel. : +30-2310-444.598
+30-2310-444.595
Fax : +30-2310-444.585
e-mail : mr-thess@the.forthnet.gr
Address : Aretsou, Kalamaria, GR-55101, Greece
VHF : Channel 9 (24 hours)

Local Port Authorities : +30-2310-444541
Thessaloniki Port Authorities : +30-2310-531504
+30-2310-531505
+30-2310-593142
+30-2310-593112
VHF : Channels 7 and 12

Click here for Thessaloniki Marina Website