There are a few places to buy trances, and trance-related toys, in Second Life. I have mentioned Mistress Elizabeth Boissay in other posts. She is a very prolific trance writer, and her trances can be found at her store, Hypnotropolis.
At the time of writing, Mistress Elizabeth is having a 50% off sale. This lasts until the end of October (that’s in 2012, if you arrive to this page after the apocalypse).
The store is located in one of those sims that disables direct teleports. You are forced to land at a central hub. Fortunately, the store can be seen from the landing position. Just turn around till you can see this view:
Mistress Elizabeth has over 200 trances, most of which are available in the ground floor of the store. (Prepare for RSI, when clicking through the vendors to view them all!) Her trances use the widely available KnK system, which is available in one of the ground floor vendors.
Also available on the ground floor are hypnosis systems and toys from other creators, such as hypnotrons and lustbaby machines.
On the upper floor, you can find RLV toys, latex outfits, and demo machines.
Mistress Elizabeth has a reward scheme for dedicated buyers of her trances:
Mistress Rewards Loyalty
First, one of the vendors holds weekly specials. The trances in this vendor are sold at 50% off; they change each week.
Second, there’s a reward scheme. You get a discount trances based on the total amount you’ve spent on Mistress Elizabeth’s trances (not counting those in the weekly specials).
This discount applies only to Mistress Elizabeth’s own products, not affiliates. The bimbo in me sees that if you were, like, to buy a lot of trances, you pay less, so buy, buy, buy! That location again is Hypnotropolis.