the store with the sewing machines is on Broadway in SoHo, on the east side of the street just south of Prince Street, I think. I go past it regularly but can't remember the precise cross streets. Go inside the store, too, as there are tons more machines on display there. Also, there are now far fewer fabric kinds of stores on the lower east side (LES) and 14th St. Stick to the garment district and the quilt stores.
where are you staying? Though I live in Manhattan, on the westside just south of Columbus Circle, I will be out of the city all summer.