Poor Roddy, its so sad to see them on their own. It took us a long time to find a friend for Tango after we lost Cash and whilst he was initially ok by the end of it he was very depressed and used to spend all day just sitting in his tunnel bless him.
Are your other two piggies boys? If so I'd strongly advise not bonding them - trios are VERY unstable and you could end up with three single piggies if theres a falling out. If they're girls then neutering Roddy would be an option if you don't want to get another pig.
On the rescue front bonding taking place over a week is completely normal and will ensure you end up with two very happy and firmly bonded chaps. If Roddy is with the rescue for a week then they can make sure he is bonded to the most suitable companion and they can oversee any teething issues etc. Whilst you can do an on the spot bond its a lot better to be as thorough as possible. If its a forum recommended rescue then Roddy would be in the best of care too so I wouldn't worry about that!