Hi drugged_beserker,
I'm sorry to say that I believe that you may be mistaken. Rome: Total War Gold edition is R:TW 1.5 and BI 1.6 included upon one DVD Disk - so really, should you already own a copy of R:TW, you might as well simply buy the expansion for money saving issue. R:TW Platinum, from my experiences, does not seem to exist.

However, R:TR Platinum, which is a modification for R:TW, can be found here. It requires a working version of R:TW 1.5, such as the version supplied in R:TW Gold to operate and completely changes the ways it works around. This modification can be found here.

Hope this helps you, cheers!