That's not an issue of font but of keyboard layout. Create your layout with e.g.
http://msdn.microsoft.com/en-us/goglobal/bb964665.aspx[
^]. Make use of the "dead character" feature.
With the many aspirated consonants of Indian alphabets, I'd prefer to create the layout for typing them the other way round - hk for ખ, thus it is sufficient to use "h" as a "dead character".