It is on Rhodium's in detail. Basicly, you drip hydrochloric acid into sulfuric acid. The sulphuric dehydrates the HCl, giving you HCl gas. Add an inline dryer and suck back trap and there you have it.
Please be careful gassing. As simple as it sounds, one mistake can flood your lab with HCl. I would guess at least 1/2 the bees who gas have some gassing disaster story (myself included). If it is possible, gas outdoors or under a fume hood.