Has a collision ever been found for SHA-1/2/3 when truncated to 128 bits?
I'm not aware of any case where somebody actually searched for such a collision.

However it would certainly be possible as the same workload ($2^{64}$) was already accomplished a few years ago (2002) by this project, having brute-forced RC5-64.

Now assume you'd use the full power of the bitcoin blockchain (300 Peta-Hashes / s = 600 Peta-Hashes /s for single hashing(19th may 2015)) you'd expect a (64-bit-)collision after 30.74 seconds ($=2^{64}/600*10^{15}$).

As noted correctly by poncho there are algorithms that help you overcome the massive amount of memory you calculated. Of particular interest would be a "memoryless" variation of Yuval's birthday attack(book page: 369, pdf page: 50 of the "Handbook of applied Cryptography").
This related question may be helpful.