Reply by Tim

Depends on the size bowls you are looking to make but you can use large gouges instead of an adze. Possibly supplement it with some carving axe chopping to get some waste out and score the grain.

Also there is a seller on eBay that sells reasonably priced adzes. I haven’t tried them myself, but reviews that I’ve found seem to be good. Here’s the seller:
https://www.ebay.com/sch/mapsyst/m.html?_nkw=&_armrs=1&_ipg=&_from=

You could also buy a vintage adze from eBay or Etsy or something like that.

I’ve had no luck finding a bowl adze from local rust hunting either in a few years of looking. They must have not been all that common.