I am not aware of the STOCK FBB being available online in any mod or d/l site.
Currently there are three flavors that I am aware of but there could be kitbashes or even higher poly versions in the works I don't know about:
1. Fury of a Seraph's fine Excelsior B LATE TMP/Early TNG Style
http://www.nightsoft.net/mckinnleystation/index.htm IMHO, for TMP FBBs this is a close to perfect as you can get using the STOCK KLINGON ACADEMY/SFC Yamato theme. She's very elegant and, yes, in a true KA/SFB/Trek scenario she WOULD be protected by a cloud of lesser support ships.
KITBASH IDEA: I'd like to see this version with Thicker warp support struts and Kodiak warp engines. IIRC SFB per Desty_Nova's SFB model site indicated that part of the problem making BBs was the size of the warp engines, you probably couldn't scale up the normal FCAs warp engines. IMHO, the Kodiak warp engines are just different enough for TMP times to overcome such a technical obstacle. Just my
2. NO MODEL: Slightly revised Textures for the stock model by Paperboy:
http://www.strategyplanet.com/sfc/ships.shtml 3. TOS flavor
http://sfc3.filefront.com/file.info?ID=27187 TOS flavor I like the warp support struts/armor that holds the four warps to the secondary hull, I'm just not a huge TOS fan. Its a great model though.
Qapla!
KF