Neil,
Congrats to own one of the classic BMWs like the M1. If I remember correctly Christopher Cross owned two M1s. One red and one white. Both in the mid-range VIN of the produced M1s. The red one some 44 VINs earlier than the white one.
As regards Taiga lightweight CSLs for sale, it's pretty limited. No RHD CSLs were really light (they all came with city pack).
From the first serie (carbs) there were no ones in Taiga. Most of them were Inka and the third most popular color was Colorado. From this first serie around 40% of the cars are traced.
Of the injection CSLs (LHD non-bat), Taiga was a pretty common color. However, from this serie, very few were really light (without city-pack).
Serie one Bats were only built in Chamonix and Polaris (+ one client request)
Serie two Bats in Taiga are less than five cars - none of them really light.
In order words, if going for a really light Taiga, I wld guess there are only some 5-7 possible cars (LHD injection, non-bat).
For the Inka and Colorado, in the really light version, there are more possible cars. I would say that here in Europe (mainly Germany, Netherlands, Switzerland, Italy, Austria etc) you will find most of the LHD cars for sale.
Cheers
Henric