It is my understanding that "potato" and "multiplier" onions are the same thing. I have never seen white ones, but the yellow ones are still fairly common around here (with the older gardeners, anyway).
I have yellow ones but currently are not available for trade. Territorial Seed Company has yellow multipliers listed in their seed catalog.
Regards,
TK

I've heard of a white shallot called 'polka' but I have never seen it offered.

I am happy to report that a friend has provided me with a small box of White Potato Onions. While they are not exactly the same as what we grew when I was a child, it will be exciting to grow them out next year and make them available to the forum members.

My friend is not on this forum and has not given me permission to list his name. He only has a small stock of the onions and once he gives permission I'll give credit where credit is due.

I will post a picture of the onions in the gallery section.

Southern Exposure Seed Exchange has white multiplier onions in their paper catalog. However, I don't see them online. Perhaps they are sold out.

Would they be the same as white potato onions?

Here is a link that might be useful: Southern Exposure

There are numerous suppliers of the white multiplying onions to be found. Think of these as "white shallots" though I'm sure I've just insulted the shallot enthusiasts.

The white multipliers rarely get much bigger than a quarter and have a finer leaf than a full size onion.

The White Potato Onion gets much larger than the multiplier and has "full sized leaves". Think of these as the "big brother" to the multipliers.

Hope this helps with the confusion.

I planted ewos last year. For some reason they struggled this year. And then the deer munched on them. Potato onions sound interesting as well. I came across this tateronion web page. I know you have a specific idea of what you are looking for, but the size of these sounded about right--and I appreciated the info provided.

Here is a link that might be useful: Tateronions

I have yellow potato onions and they aren't much difference in size/habit from picasso shallots. If anything, the shallots seem to produce somewhat more uniformly large bulbs (the potato onions were from marble to golf-ball sized, while the smallest shallots were twice as big as the smallest potato onions, the the largest were comparable between the two.) The leaves were about the same too, I did have another type of generic shallot from home depot that had smaller leaves than either and only grew to about the size of garlic cloves (but with about 30 to a clump). So maybe picasso is just a particularly big shallot.

I'd be happy to trade generously for a starter of white potato onions/shallots next summer.