Z-Wave is a mesh network system, this means that all mains-powered Z-Wave devices will repeat the Z-Wave commands - the signal can have up to 4 hops across devices. The more mains-powered devices you have in your system, the greater the range it can achieve and it will adapt to cover any 'dead spots'.
Note - only mains-powered Z-Wave devices act as repeaters as they most be permenantly 'awake'. Battery-powered devices do not repeat Z-Wave signals.
Therefore, we don't have any dedicated 'Z-Wave repeaters' as they're not necessary.
Any mains-powered Z-Wave device will automatically act as a repeater.
So even taking a Z-Wave wall plug, plugging it in and switching the mains on will give you a Z-Wave repeater. This is actually a very good solution as it can be moved around your home to help remove any 'dead-spots'.
Z-Wave Devices that act as repeaters