There's been a number of inquiries about how to keep using UVAtlas. D3DX9 in the legacy DirectX SDK continues to be the only way to currently get this functionality, which is at least somewhat tenable since it is not typically used at runtime and only
needed for building content. For the Samples Content Exporter update I'm working on to post to the MSDN Code Gallery, I'll make a control define so that you can optionally build with UVAtlas support but can live without it to avoid needing the legacy D3DX9
DLL and headers which are not present in VS 2012/2013 or the Windows 8.x SDK.
The existing code in D3DX9 is very tied to the legacy Direct3D 9 API and mesh infrastructure, and is extremely complex. Porting it is therefore not practical, and the expertise on this code is difficult to find.
If anyone is interested in rewriting the algorithm in some more modern form, the original papers that cover the algorithm implemented for UVAtlas are:
Zhou et al, "Iso-charts: Stretch-driven Mesh Parameterization using Spectral Analysis", Eurographics Symposium on Geometry Processing (2004)
Sander et al. "Signal-Specialized Parametrization" Europgraphics 2002