Are the Sweetheart Professional Model D whistles in Dymondwood with cork lined tuning slides still available anywhere? 
I’m 95% certain the Sweets stopped using dymondwood altogether due to issues with cracking. You may be able to find one used maybe post a ‘WTB’ ad on the UIE forum. I sold one a couple of months ago so there is hope for finding one used.
Those are nice whistles.
It might be worth contacting the company directly. They might have leftover stock or unmatched top and bottom sections that would play fine together.
Worth a shot but I kind of doubt it as it has been a couple years since they stopped using the material.