Have you tried using the Vri Devanagari fonts? I am sure that these have
all of the necessary characters for Pali. For dhammam one would type:

d, then (Alter+0157), then m, then M.

It is not Unicode, it uses the Windows ANSI character set. The extra
conjuct consonants are in the extended ANSI range 128-255.

I had a quick look at the Devanagari Unicode, but couldn't find the
requisite character. My memory of Devanagari is very rusty. I could read
it once, but now remember only a few characters.