Question : did it come with one, and just missing , If not was it just a 22 lr, if so you may want to check with the Manufacture make such the barrel will work with a Mag rd. There is a difference in barrels for the Mag RD. It may say on the side of the barrel. Just my 5 cents jj
My dad got a 22lr heritage about six months ago and ordered the magnum cylinder direct from them. I need to see how they work together now that you mention it. I assume it would be ok since they did not mention it but worth checking to be on the safe side.
All Heritage 22lr revolvers that don't include the magnum cylinder come with a coupon to order the magnum cylinder from Heritage. Last time I saw one it was $29.95. No fitting or timing issues like ordering one for a Ruger.