Now for those living in the US, availability is expected to begin tomorrow on the 17th of June. However over in Australia where it is already the 17th, customers will be able to purchase the device in Apple Stores around the country. As you can see in the screenshot above taken from the Australian Apple website, the device is available for purchase.
However it seems that customers will need to make a reservation before coming into the store and purchasing it. This confirms the earlier report that suggested that customers would need to make an appointment first before purchasing the watch, and that walk-ins are probably not allowed at this stage yet, presumably because Apple is still trying to get a handle on inventory.
Availability will depend on the model you are going for. For example the space grey Apple Watch with the black sport band is currently unavailable for pickup in store, but as Apple had previously stated they are planning on making it available once they have fulfilled the online pre-orders for the device.