I assume you're referring to the 50mm Sonnar and not the 85mm or 135mm Sonnars.

Zeiss Ikon used to produce push-on hoods for the 50mm Sonnar. I believe it should be A42 -- a push-on hood of 42mm, which is the outside diameter of the Sonnar.

However, these hoods can be a bit tricky for those Sonnars that have the aperture ring right up against the front nose of the lens, because there often is just a fraction of an inch for the push-on hood.

I would just bite the bullet and buy a screw-in hood. Heavystar, an eBay seller, used to offer three different hoods in the 40.5 mm thread. There was a wide, which works well with the 35mm; a solid hood, which I use with telephoto lenses but also is fine for the 50mm Sonnar; and a vented hood, which I use with nearly all of my Sonnars. These are all-metal hoods, very well made and inexpensive.