To this day, the specifics of what went down between the eras of Mega Man X and Mega Man Zero remain something of a mystery. We do have information, thanks to various data files from games and source books, but there is a certain element of seeing what happened as things shifted from one event to the next that leaves something to be desired from a visual standpoint.
One such thing is the evolution of Zero from his well-known X-series design to the one he adopted on the Game Boy Advance. Supposing you've ever had the desire to display a gradual transition through your Bandai D-Arts figures, then shrap_x may have just the thing for you.
From their Shapeways page:
For your D-Arts Zero, here is a custom mod, in the shape of Zero's saber from the Zero series. It is recommended to order the translucent version, which can be painted with clear green or blue paint, if your looking for a nice translucent piece. The first run was painted with a nice Tester Clear Green paint using an airbrush for an excellent appearance. This mod is offered with 0 markup.
Beyond this product, shrap_x also notes that another work-in-progress is a more posable model skeleton for Bandai's Mega Armor series from the late 90's and early 00's, among other projects.
As for the Z-Saber, you can find and order it (and check out other pictures) here.