I seem to remember that there isn't a Greek Amazon but Greek people use Amazon.co.uk which delivers to Greece. The postage won't be too bad - I checked it out before for someone.
It does sound like the wheel might be too small. If it's too small and hurts their back they won't use it. Once her babies have left her you could try her with the Trixie one which is probably the easiest one to get hold of online. It will be big enough and it's quite slim so won't take up too much cage space.
http://www.amazon.co.uk/Trixie-Exerc...s=Trixie+wheel
Or you could try emailing the Sugarglider site in the Uk that sells Wodent wheels - I am sure they will quote you a postage price for shipping to Greece. EU postage isn't too bad so it's worth a try!
11" Wodent Wheel (Senior) & Free Tail Guard
Hope Ginger and her little Gingers are doing fine! She will need a good wheel to tone up after her pregnancy, once she is on her own again and separated from the babies.