Is there a download somewhere for a Southwest Airlines flyable aircraft??

you could have been more specific, what type of addon you meant. Since SA is the biggest 737-800 operator, I believe what you meant was either iFly, PMDG 737 or freeware types. AVSIM library is a good however

Oops, I mean SA is the biggest 737 NG operator and AVSIM is a good start to find the right ones (especially for freeware).

Just go to the Avsim file library, select FS2004 as your search criteria, type Southwest into the search box, and go. You should pull up all kinds of downloads--dozens at least, I'd think.

If you're looking for freeware here's something to try:

 

'737exp11.zip' a nice 737-700 with vc

 

'swblue.zip' SW repaint in "Canyon Blue"

 

Search 'Moach' in the library for more on this package.