I've attached the map and the compiled .tec file. The annotation is quite bare-bones, but it does have the substitution that you want. For the most part, I've stolen the definitions from xunicode.sty (which is convenient because it has all its definitions in one place). I don't know if there are any errors in the mapping, the timestamp on this says it's from November 2009.
In any case, you'd use it like this:
%These two lines are for xunicode, if you use it instead
%\newfontface\doulos{Doulos SIL}
%\def\useTIPAfont{\doulos}
\newfontface\tipafont[Mapping=xetex-textipa]{Doulos SIL}
So in your tabular example
\begin{tabular}{r>{\tipafont}l}
1. & TA@2"DENSU \\
2. & TA@2"DENSU
\end{tabular}
It's not an environment though, just a font switch.
Hope this helps,
-Andy
xetex-textipa.map
Description: Binary data
xetex-textipa.tec
Description: Binary data
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