Greetings,
You will need a complete set of dies for 38 Special and 380 Auto. They are not interchangeable.
You cannot have too many Star machines. However, spare tool heads and shell plates are probably the best choice.
38 Special dies are common and probably someone on this Forum has a set to sell.
The 380 dies and shell plate may be a little more difficult to locate. I can machine a set of replica dies if you are unable to locate originals. Contact me via personal email for specifics.
Rich Daniels can supply you with a shell plate, I think.
There is a complete machine on AuctionArms in 380. He is asking $800.00, plus shipping.