poolbrand shock

hi I've been looking for poolbrand pool shock but sam's club in Colorado doesn't carry it anymore there selling member's mark pool shock now were can I get some poolbrand shock on line. and also I just order a sand fitler system it's a Hayward 13" sand fitler system with zeosand fitler media never used this before I know you need to backflush it but do I backflush it later after I fill the pool. i'm doing you're 7 day simple pool chemistry recipe any help need for this newbe
16ft x 48" ultra frame pool
5060 gallons
13" sand fitler system
zeosand