Anyone know a good source for some sets this fall? Thinking of planting at least 50 or so.

I don't know that I've heard of these before. We have the egyptian walking onions that set little bulbets on the top of the leaves. Those bulbets fall down and root themselves on the ground. Is that what you are talking about?

Nope

I found two sites, at least that are showing dutch multiplier onions.

This one has seeds
http://www.richters.com/Docume...

This one is not accepting orders again until spring.
http://www.fedcoseeds.com/moos...

Yellow Moon Dutch Shallots Allium cepa (aggregatum group) Also called Multiplier Onions. Beautiful vigorous plant with many onion-like leaves, good as green onions (scallions) in spring and early summer. Beefy yellow bulbs with good skin quality mature early. For large shallots, maintain high fertility and steady moisture. Outstanding storage quality.

I don't know if this is what you are looking for .... but just had to look.

They are out of stock on the multiple bulbs in a clump under ground type. I like those because of the great flavor sauteed or in soups. U plant 1 small bulb in fall next fall dig up a big bulb surrounded by sets. They store really well also.