I have a copy of the SDK on my hard drive, so it was eventually made available. I can't remember how I got it. The .svn data in it points to the original source being https://ugobe.svn.cvsdude.com/pdk/trunk and the creator being user tylerwilson. Here is a list of all the files. As far as I can tell from Wikipedia, Jetta Company Limited is likely the owner of the Pleo IP, and I am uncomfortable making the SDK available without their permission. If someone has a contact at Jetta who might be able to help me get permission, I will be happy to make the SDK available.