Never seen a single point sling with any type of holder built in.
This type of sling works best with short and lightweight firearms, especially the MP-5 and other SMGs, and not bad with carbines like the M-4.
If your shotgun has an extended tube magazine it may strike your shins or knees painfully as it swings around; even if you do have a weapon catch on your belt or harness it can be difficult to secure it at times.
Depending on what type of sling you want you may need a mounting plate that bolts between the stock and receiver.
Just a few things to consider...
