I have searched for the Tokina 50-135mm lens (Canon mount) for some time, but it has been elusive. Distributors said it remained in production but would have to be "ordered in" most likely (with a huge mark up!!!). It appears that most of the output is going to Japan/Pentax/? research going into Sony mounts. There are rumours of an IS lens appearing at some stage - but I wonder if this is just hearsay. Because I do a lot informal portrait photography, the range of this lens is perfect and at F2.8 it would be fast enough for low light, with or without IS. I would look at Sigma but it suffers some pretty average feed back from real users.
I do have a Canon 70-200 F4, but is a bit conspicious at times! See what variegate opinions might amass.