What are the current options for short crank arms?
There aren't many options out there for cranks shorter than 165mm. Your best bet is to buy a set of longer crankarms and get them shortened at a service like Bikesmith Design.

Also, if you are legitimately having knee problems, I'd suggest that you find a professional fit service in your area and have a fitting done. The length of your cranks may not be the issue, but it may be the size of your frame, position of seat, etc. Online calculators can be good, but a professional service will certainly address these issues in a more targeted way and perhaps save you from spending unnecessary money, modifications to parts and perhaps save you a lifetime of pain or discomfort.