The half crown series of Great Britain is an interesting one. Although crown pieces circulated, I suspect that they were relative rare in circulation, just as is the half dollar is scarce in circulation in the U.S. I am currently looking for a young head shield type. Other than that, the type set of British half crowns that I am building is complete from George 111 to current.
I have an almost complete set of all the major types of shilling, going back to Henry V111, and that is also an absorbing and interesting series, well worth numismatic study.