No US carrier has released 4.5 yet for any device. All you can get is 4.3 on devices released in the last 6 months or so like the 8120, 8130, 8330. Any device released since about Jan should have 4.3. Any device released before that most likely has 4.2.
And like everyone said, just download one of the 80 million (un)released betas or one of the few officially released 4.5 OS's. Just delete the vedor file and have fun. Just don't put any 4.5.0.37 on your TMO device cause it will kill the sim repeatedly.