In the US and Europe, the trade in wild-caught chameleons is quite extensive.
Sources state that 476000 chameleons were exported from Africa (including Madagascar) to the US and Europe between 1993-1998.
With the pet reptile industry even bigger a decade later, I'm pretty sure the number of animals exported now is even larger.
Most of these wild-caught animals are distributed to pet stores, or online retailers. Most of them have a very short lifespan in captivity.
However, you'll find that the majority of keepers on these forums have Veiled chameleons or Panther chameleons. These two species in particular are bred extensively in captivity, and it is these captive-bred populations that make up the majority of animals in the pet trade.
In fact, the pet trade of chameleons has grown so much in the US, that breeders there have really large-scale breeding programmes. In fact, Jim Flaherty of the Chameleon Company said that he bred and sold about 6000 chameleons in the last year!
Correction... Jim did not breed 6000 chams last year: "Our goal with the one greenhouse is about 6000 per year. We aren't there yet." Still, it's a big operation.
All of the online retailers, and most of the pet stores will indicate to the buyer whether the animal is captive-bred (CB) or wild-caught (WC). Most of the information you will find on the 'net, as well as the advice given on these forums, discourages keepers from buying WC chameleons. They do not do well in captivity, and are best left for experienced breeders/researchers who are trying to establish new captive-bred populations.
In South Africa, the legal situation regarding indigenous/wild-caught reptiles is still a bit uncertain, because various provinces have different requirements.
For instance, in Gauteng, not only is it illegal to keep indigenous reptiles, it is also illegal to catch them or to transport them.
It is highly unlikely that you will find any pet stores selling indigenous, wild-caught chameleons in South Africa.
The various branches of the Department of Agriculture have adopted quite a hard-line approach to the wild animal trade, and in the last couple of years, they have begun to focus on reptiles. There is still trade of wild-caught SA reptiles occurring, in particular venomous snakes, but the industry has become a lot more regulated, with the SPCA getting involved too.
At all the reptile expo's I've attended in Johannesburg in the last year, the only chameleons for sale were captive-bred Veiled chameleons. Some breeders are working with Jacksons and Panthers, but they haven't really come onto the general market yet.
So, the bottom line is that there is NO justification for keeping a wild-caught chameleon (with the exception of Hawaii maybe, where they have become a pest almost).
In fact, by supporting pet stores and breeders that sell captive-bred chameleons, you help support the development of more captive-breeding programmes. If enough captive-breeding programmes exist to sustain the pet industry, this might eventually help to slow or halt the removal of wild-caught specimens from their natural environment.