I'd heard, late last year from a pretty reliable source, that there is a genuine, promising, lead, but there are problems in recovering the episodes - if they do exist - which have now been dragging on for months.
What kind of problems?
At a guess, not knowing the specifics of this situation, it's probably two things.
Second, legal immunity.
The first one's kind of obvious -- the person, theoretically, has something the BBC wants. The BBC would claim, "That's our property you have." The person who has the cannisters, however, may not view it that way. He may want either money to exchange hands or for the BBC to return the film to him once they've made duplicates. The BBC may not be willing to do either.
The second one isn't obvious, but I've heard it cited before in other returns. The films that were sent overseas were BBC property. If someone held on to them rather than returning them or destroying them, they're stolen goods and the person who has them could be prosecuted. The owner might be willing to give them back to the BBC (either gratis or with a price attached) in exchange for no criminal charges.
In short, the legal issues on this would be a murky Gordian knot.