In game, not so rare. As mentioned, everyone should win atleast one, and they do appear in the UCD somewhat frequently. At least for me, anyhow.
In real life, as also mentioned, it may be more rare. It is the first production turbocharged Beemer afterall, and as such likely a big thing when it appeared in dealerships. When you factor in the number of the Turbo 2002's which subsequently mated with an Oak tree, general use & abuse, neglect, and just age... not many are probably around in good nick. Also factoring in are engine swaps and power-adders, which likely often find themselves in a standard 2002, it can become even more rare.