JF,
Look for the Brenneke slugs. I bought the Home Defense rifled slugs for use in my Benelli SuperNova Tactical. Ammo to Go has 100 rounds for about $1.00 per slug. Use the Rifled Version for the Tactical Smooth Bore Barrel. Federal. Fiocchi, Remington, and Winchester make "Managed Recoil Rifled Slugs." I purchased some WinLite Low Recoil 00 Buck (WL1200) and Royal Buck Low Recoil 00 Buck (RBLR129). Both have 9 pellets and sell for $4.99 for a box of 5.
I also purchased some Remington Managed-Recoil STS Target Loads, 2 3/4", 1100 FPS, 7/8 oz. 8 1/2 shot (RLSTS1285) and Winchester AA Xtra-Lite Target Loads, 2 3/4", 1200 FPS, 1 oz. 9 shot. Bass Pro has the Remington at a reasonable price for a case of 250 shells, and Gander Mountain was also reaonable for the Winchester Xtra-Lite Loads.
I think Fiocchi and Winchester also offer similar loads at a lower recoil at 980 FPS. You may need to order the 980FPS shells on line.
captnkc