organized clubs for motorcycles in general yes .
but they are mostly touring clubs , a few of them organize events for mx or enduro only .
there is nothing for trials i thing . there was a greek trials championship until 2010 but all the events (3) where in athens . i am a beginner in trials so not the right person to ask ...
the terrain is great , you are going to love it . in mainland or islands greece is an off-road paradise , perfect for enduro or trials , there are no laws to stop you from going almost everythere you like , except beaches and personal properties . all the forests and mountains are almost free for every motorized sport .
my home in near a forest so my trials playground is a half mile away !!!
trials holidays in greece ?
come on , get serious (hehe) ... we are in the middle of a crisis .