Although the PPV is no longer made, there are similar inexpensive 2-seat trikes such as this one:
http://www.trailmate.com/productDoubleSpecial.cfm

Sun bicycles makes a Quad from two single recumbents bolted together.

http://www.sunbicycles.com/03/html_04/recumbents/ez1_sx.html

Just Two Bikes has a similar arrangement for their SWB recumbents

http://www.justtwobikes.com/

Rhodes car makes 4 wheel Pedicabs and Surreys for recreational riding

http://www.rhoadescar.com/

Lightfoot cycles builds production and custom vehicles for all types of practical transport

http://www.lightfootcycles.com/

This isn't the only weird pedal vehicle I own. You can see my others here:

http://bikelist.org/seawheels/NicksBikes/NicksBikes.htm

 
If you know of any links to anything PPV-related send them to me at nick.hein@verizon.net