Guardians of Harmony will apparently be heading to the UK and release at the same official time as us here in the USA at Smyths. They don't have them listed on the website yet, but I'm sure they will soon if they end up doing pre-orders. Have the email response they sent to a few people that asked:
Thank you for your email.
I can confirm that this particular range will be available in Smyths Toy Store from September.
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.
Thanks to Samuel and Lian for the heads up!