There have been twinned Holgas in the past (holgamods.com offered one for sale).  But at the 2008 Photokina, Universal Electronics Group actually displayed a pair of stereo cameras.  Stereoscopy.com had this to say (and a photograph of them, too):

This company is exhibiting two pre-production models of Holga Medium Format Stereo Cameras.
One model, the Holga 120 GCF 3D, has a 67 mm stereo base and an image format of approximately 54 x 53 mm (HxW). The lenses are cheap 1:8 f/60mm lenses
The second model, the Holga 120 PC-3D is a pinhole camera, with a pinhole of 0.3 mm and f 135.
Prices and availability are not known yet.

Anyone who expects these to have sharp lenses or light-tight bodies is probably going to disappointed, but they could still be fun to play with.  Since Holgas sell for $20, maybe these will go for less than $50.