Hi Gert,
I don't know if I can buy an MEK type adhesive here, but plastic model cement of some type should be available in a model shop near you (if they sell plastic models). We have something called Duco cement and Wal-Mart sells a generic equivalent. I believe Graupner sold the appropriate adhesive. Straight acetone will soften/dissolve the plastic, but it will never harden - just stay a gooey mess.
Good Luck,
Will