If you are in UK, you can now register your interest for Lumia 830 and Lumia 735 on many retailers and carriers.
Clove has both of them listed as “on pre-order”, but you can at most register to be notified.
CarphoneWarehouse also has both of them listed as coming soon and expected release date is “October 2014”.
O2 only has Lumia 735 listed as coming soon and you can register your interest.
