look at Purina one sensitive systems, its a combination skin and stomach based care food that is salmon based
They also have a lamb-based formula. My Springers did fine on the salmon but after a while just refused to eat it. Their breath was also awful. The are fine on the lamb.
The rescue got her late Sunday evening, they took her to the vet Monday and got her checked out and spayed and we adopted her Wednesday so she was only there a few days but they had her on Natures Select and sent some home with us. I'm using that for now, haven't decided whether to continue or not.
I'm also in the camp of "if it ain't broke, don't fix it". If it's an issue of cost, compare ingredients with other brands and try to find one that matches.
Congrats on being rescued!