Best place, probably ebay. people just want to get rid of the broken stuff sometimes.
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there is a parts or not working filter too. https://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=iphone&_dcat=9355&rt=nc&LH_ItemCondition=7000&_trksid=p2045573.m1684