They are advertised all over Kijiji and Craigslist - just wanted to make sure that the 3rd generation only came in 32 and 64GB.
Here is the kb entry for the technical specification of the 3rd gen ipod touch. There are only 32 and 64 GB Models.
This support page from Apple explains how to identify iPod models. I do not see a 3rd generation iPod Touch with a capacity of 8GB on this list.
Working from memory here, so I could be mistaken, but at the time the third generation iPod touches came out, Apple released 32 and 64 GB models. It continued selling the second generation 8GB model alongside them. Someone who ordered an 8GB touch at the time when third generation models were on sale might well believe they have a third generation iPod touch, but there was no refresh of the 8GB model at that time.
In 2008, the second generation iPod touch was released, in 8 and 32GB sizes. The next year, the third generation was released with 32 and 64GB. The 8GB 2g was sold alongside it, probably to make it look cheaper. This model doesn't have multitasking or homescreen wallpaper support, nor can it be upgraded past iOS 4.2.1. I do agree that this was confusing, and it even confused me when I bought the 8GB 2g.
You can identify if a touch 2g was bought before or after the 3g like so: go to Settings, General and About. Scroll down to the model; if it starts with MB, it's the older model. The 2g also has
A1288 printed on the back of the device.