According to Sony, all it's Playstation VR stock that was allocated for pre-orders have been snapped up. I haven't seen anything that definitively states that there will be zero PSVR units available for general sale upon the October 13 release, but I would be surprised if there are more than a handful. It makes sense that Sony and retailers would want to lock in the sales through pre-orders. Still, there will certainly be a few people that cancel their pre-orders. You might want to contact you local Gamestop and see if you can get on a waiting list in case someone cancels.
Of course, some of those people with pre-orders will turn around sell them on eBay for double the list price, so if you really want one right away and are willing to pay, that might be your best option. I just hate to encourage profiteers from taking advantage of demand and reselling units at inflated prices.