If okorder / Any 6 shot 41 caliber speedloader should work. Can't you use the same speedloader as an SW Model 57? Try asking this question to HKS.
Welcome to my world. The bathroom is the second door on your left. There are literally hundreds of revolvers HKS does not make speed loaders for. People who need speedloaders always buy a revolver that they make 'em for. You look at the list, then, buy the firearm.
Call your local gun shop and tell them your first sentence. They may have one or more on hand or can get as many as you want within a reasonable amount of time.