Savage 64 TR-SR thread length and Sparrow

I bought a Savage 64 TR-SR for the threaded barrel, and when I try to screw on my SilencerCo Sparrow, it bottoms out before touching the shoulder of the barrel. I know a spacer is needed, but all the ones I have looked at seem too thick. I dont want peel washers, but a spacer that is machined for the correct purpose. Has anyone found a good spacer, preferably threaded, for this purpose? The link is to the 64 TR-SR so everyone will know which rifle Im talking about

http://www.savagearms.com/firearms/model/64TRSR

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