The Google Nexus 7 tablet is selling quite well, the 16GB ($249) version has been sold out  and the Play Store states it as as “coming soon” in the US and the UK. Well there is a Notify Me option for the 16GB one, so people interested will be notified with an email whenever its available.

The 8GB ($199) version is still available and is shipping in 3-5 days.  The reason that the 16GB model is selling out fast could be the thin margin between the 8GB and the 16GB, also may be due to lack of expandable memory option.

Source 1 | Source 2