Vendors of Nebuka bunching onions always show a photo of bunching onions with bulbs that are much larger than the normal slim bunching onions bulbs. Has anyone grown Nebuka and produced these larger than normal bulbs...or is this just a wishful thinking type of advertising?

I've never grown that variety, but looking at the pictures, they look smaller than bulbs I've gotten from Crimson Forest. So, I'm inclined to believe it.

Here's an eBay link that has the photo I'm referring to. Is your Crimson Forest bulb larger still?
https://www.ebay.com/itm/175203874268?var=474735368986

I'm still looking for someone who's experienced the large bulb size with Nebuka bunching onions? Anyone...?

That may be true of ebay and etsy vendors but that is not the case for your seed vendors. Most all of them show long slendor green onions and state that they do not form balls. An example, Victory Seed states that this onion does not form balls under most conditions. https://victoryseeds.com/products/nebuk ... hing-onion. Same with Reimer Seeds.

If you are looking for a bunching onion that does form balls, then try He Shi Ko bunching onion.