There's quite a bit of info about these that you can find here on GardenWeb. Here are the search results:

Here is a link that might be useful: Search Results for

Link description should read: Search Results for "potato onion"

Well, I really messed that up. Even the link is wrong. Here it is again, and hopefully it will work right this time:

Here is a link that might be useful: Correct Link....hopefully

Here is a source, but they ship potato onions in the fall.

I have ordered my seed from them for several years. I have also ordered garlic, and have had no problems.

Here is a link that might be useful: Southern Exposure-Potato onion