I got my insert and chain from Samorga. Samorga makes incredible gold chains. It looks identical to the original YSL chain (I'm very picky). Mine is the 40in. Will post pics tomorrow in better lighting. But here's the link.
https://samorga.com/shop-2/bag-accessory/4-flatten-cut-4-way-flattened-cut-chain-crossbody-strap/
https://samorga.com/shop-2/bag-accessory/4-flatten-cut-4-way-flattened-cut-chain-crossbody-strap/