Well gentlemen, let's not be too hasty in dismissing this entirely. We DO have a few examples of leather armour with no visible metal reinforcement from the 14th century, one of them being this amazing effigy with leather arms and leather legs.
https://www.flickr.com/photos/roelipilami/1623517375/in/set-72157602468647900/Note how his greaves are laced together and how there are no discernable hinges on the fully enclosing arm harness. Furthermore, there are no lines or rivets to indicate splints. At most, the ridges have something to do with a splinted defense, but there is nothing much that speaks for it.
Furthermore, we also have the bazubands found in Estonia:
http://im1.shutterfly.com/media/47a1cc38b3127ccefeb2e27de0eb00000040O02AaOXDNq5btAe3nwc/cC/f%3D0/ps%3D50/r%3D0/rx%3D720/ry%3D480/They do not seem to have metal bands, the rivets appear to be only for decoration. The shape matches those seen on German effigies at the time (although those do have metal bands on the outside at least).
Then there are stained glass windows from Munster in Germany
http://www.soniahalliday.com/images/GE99-2-12.jpghttp://www.soniahalliday.com/images/GE99-6-12.jpgThere's also the standing collar worn outside of maille on an effigy on a German church, again, 14th century.
http://s196.photobucket.com/user/shinumo/media/Wells2.jpg.htmlNow, the difficult thing is the body, since I have no sources for body armours exclusively made out of leather. However. There are plenty of examples of coats of plate being made, seemingly with a leather outer shell, this means that, to get a good 14th century impression, all in leather, you could simply make the outer shell and add a charming rivet pattern. Sure, you won't get the visible edges of metallic armour underneath, but it will certainly look good enough and, again, be made entirely out of leather.
Some inspiration for your rivets:
http://www.hoashantverk.se/hantverk/hoas_rustningar/These are all reconstructions of the Wisby armours. As such, they'd be great for a period of about 1330-1345-ish for knights and later for foot soldiers.
I hope this helped in your quest for leather! There are some more examples out there of knights with elaborate patterns carved into their rearbraces and into what some people believe to be a leather covering for kneecops, one effigy in particular stands out, but I can't bring him to mind.
Edit: Found some more leather armour:
Italian painting from 1350 to 1370, most googlings turn up 1357.
http://www.wga.hu/art/l/lorenzo/venezian/predell1.jpgCuir bouili rearbracer, second/third quarter from museum Somethingsomething in London:
http://www.vikingsword.com/vb/attachment.php?attachmentid=52277&stc=1