Oscar De La Huerte answered

Because of this, there is something of a booming market for people selling their used undergarments.
Where to buy used panties
There are a million and one women out there who, to earn a quick buck or two, are turning to the internet to flog their used undergarments.
This means that there are a whole number of sites to choose from. But here are a few that I'd suggest:
- eBare.co.uk- Based on the popular auction site eBay, this web portal is dedicated to selling objects of a sexual nature (including used panties).
- Penelope Hart- Basically any woman's name followed by usedpanties.com seems to return a search result, but this is one that I found particularly appealing.
- LondonFetishScene.com- Most big cities have an online fetish community, and this is one example. These sites usually have classified sections, chat facilities, and forums. You are bound to find someone willing to sell their used undergarments on this type of website.

- Health and safety- there's no need to be too obvious about this, but there are certain risks involved with buying used undergarments.
Whilst I believe everyone is free to express their sexuality however they please, I'm not sure people should be putting their health at risk.
- Value for money- I would recommend that you shop around and make sure you are getting the best value for the money for what you are buying.
On the other hand, there are quite a few online communities and personal blogs where real-life women sell their underwear.
I'd assume that these would be more gratifying because there is also a human connection associated with the underwear that's for sale.
Buying from this type of outlet also means that you may receive correspondence - and even photographs of the women in question modelling the underwear for sale.