Hi Nikolav! welcome to our forum!
sure there are a few aquaristic shops in thessaloniki that include marine aquarium products and sealife as well. here are the telephone numbers and e-mail addresses of most pet shops in Thessaloniki (not all of them combine fresh and saltwater)
http://www.aquatek.gr/vb/showpost.ph...03&postcount=2 and
http://www.e-leoforos.gr/index.php?o...144&Itemid=413 i think it wouldnt be a problem to contact them by phone.
some i can recall right now that do have a site are
www.azores.gr and
www.quiko.gr . if you use a search engine i suppose you will get some more...
p.s. Do you purchase any products from the internet? there are quite a few "cheap" on-line shops.