A quick search does not present any results for a viewer to display .MPO files in anaglyph form. This would be due to the original method of creation. The .MPO type was created to accept images generated by dual-lens cameras or the equivalent, which of course, would not have red/green or red/blue capability.
If you use a "standard" viewer for .MPO files, which display the image in left/right format, it is stereoscopic but only if you use a split-lens type viewer. The software will not generate a stereoscopic image viewable by unaided eyeballs.
I suppose one could stretch the reasoning a bit and create an image format that would be viewable on the niche-market 3D tablets and/or televisions, but that's certainly not the scope of your question.
By searching for "convert .MPO to anaglyph" I located a number of programs that will take the dual images and color-convert them to the typical red/green or red/blue anaglyph you seek.
These are not viewers, per se, but may be the only option available to you, considering the constraints inherent in the .MPO file format.