Evidently Stein's doesn't carry these items. Jung's in Point may be an option , but I'm not sure.
What is 'Super Thrive"?

Pick & Save here in Milwaukee carries the fingerling potatoes...you might try them there and see if you can find them. Superthrive here is carried by Stein's Garden Centers.

Dave

See if you can contact Keune farm. They are north of appleton. They sell their produce at The Free Market on Wisconsin Ave. in Appleton and at the Red Radish in Neenah. They would have Keune's number. I buy their fingerling potatoes at the Red Radish. Also, Pansies Country Store on Cecil St in Neenah sells seed potatoes.

Pansies: 722.0574
Free Market: 968.1260

Hope this helps!

cheers,
NoraBelle

Jung's in Point, does have the fingerlings. I have not seen the superthrive.
Happy Gardening