Can I buy a 24v transformer with a dedicated common c-wire feed?
Um, I don't know where you got the term "power stealing".  What you describe as that, is exactly the normal way to do that thing, and the right way... unless you are aware of some capacity issue on the transformer (as is sometimes seen in transformer-relay combos).  

As far as the R and C terminals, any HVAC transformer has two pins on the 24V side... They are R and C.  The one that is not R is C.