I just repainted my decks with Interlux Brightside, flattening agent, and added SharkGrip anti-skid, available from Sherwin Williams. If I had to do it over again, I would have used Interdeck, because the cost of the individual components adds up quickly.
However the SharkGrip is spherical polymers that stays mixed in paint like Intergrip, but at about a third of the cost. You use very little of it and its more readily available than Intergrip.