Schlage A series extension link. The link is compatible with a 10" backset and the parts are no longer available and very hard to find.
Please note: in order to obtain the 10" backset the extension link must be used in conjunction with a
2 3/8" spring latch or dead latch. The latch is not included with the extension link in the listing and must be purchased separately. I can sell you a latch if needed.