I was at Sportco this afternoon and saw the following specialty slugs. Must have received a new shipment since you were there last.

Hornady H2K's
Remington all copper sabots
Federal Hydrashoks 1 oz.
Federal Barnes X sabots in both 3/4 and 1 oz.

That along with the Rottweil slugs (very accurate because of the stabilizer) should give you a good selection if you can make it up to Sportco. You might have purchased a Mossberg Model 500. It is a 3" gun. All barrels for the 835 are 3.5" barrels.