G'day Mike,
ya need 2 things:
1) a font that has a flat symbol in it and
2) the ASCII code or letter equivalence for it...

There are lots of fonts around that will do the job. Most of them come with notation applications. If you look at the Noteworthy Composer Scriptorium: www.nwc-scriptorium.org you will fine a "helpful files" link that will take you to a selection of files - some of which are fonts and some of those include the symbols you are looking for. You will also find some font suites that I've put together specifically for NWC2 but which are usable in other applications too.

--=-- My credo: If it's worth doing, it's worth overdoing - just ask my missus, she'll tell ya laugh --=--
You're only paranoid if you're wrong!