I haven’t seen them personally, but there are some documented cases I found on the Net: A vending machine that promises the chance to win a PSP, but dispenses mostly underpants (presumably in mint condition).

But more to the point there is this case where someone actually made a second-hand report of a panty vending machine in 2002. Complete with a photo, but of course it is possible to doctor it:

According to the PhotoMann article, a used underpants costs 1000 – 3000 Yen if bought from this machine (6.10 – 18.30 Euro).

InventorSpot has some additional photos and points out that a vending machine that sells panties doesn’t mean that the panties are used.

However, my sources in Japan say that these vending machines really exist.

According to the JMate article, a company called Genyo produced this as a “shoulder massager” in 1997. The design was approved by Sanrio, the owner of Hello Kitty. The item was not officially intended for any “adult” purposes, but of course people quickly put the vibrating thing to other uses. By 1999 it had become a cult item in Japanese porn movies. Sanrio was less than happy, and eventually found an excuse to seize and destroy the molds.

This means that you’re probably out of luck if you want one of these, but it seems they are sometimes auctioned on eBay.