You might try one of the flotilla companies: they have tightly-packed compounds, but might care to fit you in. You would need to chat up the local manager, who will be in charge of the organising of lay-up. Nielsen, based at Nidri, are a good outfit. If you want to PM me, I might be able to give you more detail.
Sunsail at Vounaki also offer visitors laying up
or that was the case if you bought an ex sunsail boat from them
and i think there were other visitors there too.
<hr width=100% size=1><font color=red>Have you seen the flippin forecast!</font color=red>
A number of us have kept our boats with George Tsiligiris at Preveza Marine, a few clicks north of Levkas town on the mainland so great flights etc in and out. Service is excellent and very friendly. Can't rate them high enough.