That would be some function, with all of Unicode...
For a more limited set, you could use simply =
Middle ( alpha ; code ; 1 )
where alpha is your set of characters, e.g.
I'm trying to produce Char(9) in filemaker 9
For that, you could make a custom function called Tab, and it would be simply:
Copy a tab character in any application (in Filemaker, type Option-Tab into a field and copy) and paste it in between the quotes.