I received a reply today, and here's the copy/paste version of it:
Thank you for your email
I can confirm that the Generations Fall of Cybertron will be available later this summer and will not be an exclusive to any store. The Voyager range will be coming to the UK in 2013.
May we thank you for contacting Hasbro and if we can be of any further assistance, either now or in the future, please do not hesitate to contact us again.
Hasbro UK Ltd
So there you have it. Keep in mind that it is from Hasbro UK, so take it all with a pinch of salt, but it certainly sounds like the search for Shockwave isn't going to be as painful as we were initially expecting!