Railed mag/barrel clamp w/ sling swivel?

[kagia]

A friend is looking to replace the factory mag/barrel clamp on his Remington 870 Tactical with a railed aftermarket clamp system, but also would like one with a sling swivel like the factory one has.

Are there any mag/barrel clamps out there which have a short rail on one side and a sling swivel on the other?

Thanks.