How tall are you? Schwinn (straight bar) Heavy Dutis have a actual 22 inch top tube and an effective 23 inch top tube.
They are still available new. Use their store locator to find a shop near you. If they don't have one they can order one for you.
Store Locator | Schwinn Bicycles
If you are looking for the "king Size" American or Heavy Duti, which was a cantilever, I believe those were only made in 1962-1965, and finding one of those would be tough.
I'd sell you mine, but I've put to much love ($) into her.
