Bridging finance is difficult to arrange as it depends entirely on affordability. If your friend can afford a mortgage of 350k then it shouldn't be a problem, otherwise he'll be lucky to get it.
Interest free bridging does not exist but it is possible to get it at homeloan rates
I do not know about credit unions
He might want to think about setting up the property he plans to sell as an investment property that he is going to rent out. This could help him get it approved if he's having difficulty