I would contact
Altman directly for if they have any replacement shutters that would be of the same type just different model type such as the 6-30 style.
If they don't, in my observation it's fairly rare that replacement shutters for such fixtures are ever really needed. Can they be cleaned up if not re-surfaced? Do a search on the website for resurfacing shutters. Otherwise if trashed and not available, your local welding shop should sufficiently be able to reproduce a stainless steel version of these shutters without a problem given a plasma or water cutter. Won't be cheap but should last for years.
Good luck but my theory is the shutters most likely on the fixture can be saved to the extent you will use them in the future given the extent of other fixtures available.