Is your vet requiring payment up front? before they see the dog?
Most clinics (in my experience any way) require payment when the dog is discharged from the clinic that could be the same day or days later. Many place may require a deposit if the estimate for treatment is going to be expensive.
I would call them back, let them know how ill the dog is and get ALL the payment requirements.
You can actually apply for care credit on the phone or over the internet, and you get an answer pretty quick, like in minutes.
I would go online and do that now, if you are approved you can get him there tomorrow or even to an emergency vet tonight if you so choose.
Call all the other places mentioned also, even ask your vets office if they know of any other agencies or local organizations that help with things like this.
I wish you luck, keep us posted, I hope you are able to get him in soon.