If you go to Plantscout on database and search each variety name of the iris you are looking for you can often find for most cultivars have a profile page detailing that cultivar with comments/recommendations as well as postings of people either offering or looking for that particular cultivar. You then can pursue contacting the individuals looking for that plant. For example checked on the tradlists an there people offering 'Belvi Queen' on there

Might help you in your search. I'm sure there are mail order places that carry them as well.