If you have an Ace Hardware nearby you can buy the bolts and the u clips there. I picked up a set too and got everything I needed at Ace. I also bought harder bolts.
Here are the sizes right out of the MOPAR Parts catalog, you will need four pairs of bolts and u nuts and four smaller nuts:
BOLT AND WASHER, Hex Head,M8X1.25X25.00
NUT AND WASHER, Hex, M6X1.00
Two 8MM bolts hold the rails using the two 8mm u nuts. Get two 6mm nuts either with a washer or flanged. They hold the rails to the sills so you can securely mount the rails using the larger bolts.
So altogether you need four 8mm bolts, four 8mm u nuts and four 6mm nuts with a washer or a flange.