i've encountered the same problem (i think)
if you cant find the .blp file to extract from the SpellBreaker open up the .mdx file with a word prossesing program (word, note pad, etc.)
and open the EDIT bar and select find and look for units (if that doesn't work search for textures) if it comes up with the Unit search it should look like this (or something)
unts/human/spellbreaker/spellbreaker.blp
fot textures:
Texture/Spellbreaker.blp
and the one it comes up with are .blp file you need to extract.