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I may be alone with this opinion but one of the best snare strainers I've ever owned and used came standard on my D505 in 1983.
Built well with a simple well made throw handle and knurled tension knob paired with a solid fine adjustment on the butt end.
I wonder if they have any spares at the factory they would sell? 
They have long been sold-out of all that stuff. They keep spare parts a few years and that's it. If they have any on hand they aren't for sale. I recently looked in to a bunch of old parts and they just don't keep obsolete parts around beyond a certain warranty period.
I personally think the Dual Glide System is the top of the heap. My only complaint is that the small adjustment knobs are are to grab. If they were knurled, it would really help.