From what little I know, the Turbo Rat seems to be a more modernised version of the Rat. It does seem to have been in production for quite a while, so the "rarity" issue would appear to be clutching at straws (to me anyway!).
Many years ago, I had a "Vintage Rat", which was a reissue of the original circuit by ProCo. It did have the LM308 in it, but how accurate (accu-RAT?) it was I have no idea. I do wish I'd kept it, they only seem to have produced it for a few years in the mid-late 90's, and finding another one is testing (and expensive).
There would seem to be more readily available "replica" Rats by the myriad boutique pedal makers, at various price points.