I keep hearing this rumour, what is it?
I mean it's likely either a hoax or someone mishearing the source of the 2011 discoveries was (likely) Australia.
I keep "hearing" the rumor too. No idea if it's true.
But Oz was the main place, outside of the UK, that got Doctor Who episodes in that era (as a former colony?), and thus likelier to have them still around somewhere.
I think the hope is, they
didn't destroy them.
The US didn't get anything till the mid 70's, I think, so probably no chance any of those missing eps are here.
A large chunk of the Australian episodes were sent back to the UK in 1975. A handful of episodes (The Chase 1, The Celestial Toymaker 4, The War Machines 2 and The Faceless Ones 1 off the top of my head) stayed in Australia. Others were confirmed as destroyed or sent to New Zealand (in terms of missing stories only The Reign of Terror was in this batch, and the NZBC destroyed these copies in 1971).
In terms of main buyers, Australia, New Zealand and Singapore (and later Hong Kong) were the big broadcasters. Singapore in particular as they're the last known buyers of such stories as The Tenth Planet and The Power of the Daleks...
Sierra Leone retained a batch of most of Season Three but their archive was destroyed in a civil war in 1999.