Are there combo handheld radios for CB and amateur radio? If so, is it practical?
No, there are not, because it is not legal to have a radio that can transmit in both CB and amateur radio bands.
To be legal, CB radios must be part 95 type accepted. The FCC prohibits a device to be both part 95 type accepted and capable of being used in amateur radio frequencies.
Having said that, many amateur radios are also wide band receivers, and can receive CB.