Welcome Mick!
I don't really know any euro country that will openly sell you otc diazepam. Some of them do so with Lyrica, tho.
But anyway if you want to travel with your methadone, I remember the Methadone World Wide Travel Guide, in a site called INDRO. I am not sure if it still works, I'm talking years ago.
Said place told you the legal situation of mdone in each country, one by one, and resources for it, if there were.
Also, will they only give you doses for two weeks? I have been allowed to have 30 days worth of it with me when travelling to other countries.
I hope you find a nice destination and enjoy your time.