radiator

Take it to a radiator shop, if it can be repaired it will be cheaper than buying new. If you do have to get a new one there's a lot better chance it will be right than from a chain parts store.

Try radiatorexpress.com. They usually have what I need for a good price.

hmmm, is there a pickup, van, or medium duty truck equivalent tor workhorse?
Like with Ford, even F53 motorhome stuff can often be found at napa or autozone, searching under E450 or F550 trucks.

Did you try Autozone. It may be a special order though.

Any Chevy truck dealer.

You could check OMEYS website they are a good source of info for workhorse, they may be able to tell you where to find one.. Fleetwood also still has info for workhorse

NAPA but they are high on prices, ask at a truck shop for names. Is yours repairable? A good radiator shop can fix or recore.

At any radiator shop.