If you know the name of the company you could try calling them, otherwise you have to wait for store to reopen. You mean its closed for the day don't you? If its closed for good then you have to remember the pet chip company name and call them up and go from there.
Also try calling the local shelter and spca and then you can call around to vet clinics, most all of these places (minus the scum shelter) will take your info down and contact you if they find your dog. But keep an eye out for the shelter, ours here destroys dogs after like 4 days... =(
Good luck. Also of course i'm sure you thought of it, but if by some chance you had the receipt, it'd probably have the pet chip number on it.