Richardson Electronics has a few of these cut to about 18" length. They call it a 6274-17.875 and they're selling them for around $50. I bought two for my hybrid amp project- particularly liked all the thermal mass and conductivity in the over 0.5" thick backplate and if anybody is interested in a heavy duty flat plate heatsink with 0.8 degree C/Watt performance per 3" length, Richardson seems to have a few left as of the time of this post.