Looking for pettiblouses or petticoats? This is where I’ve found them for sale.
A pettiblouse (or blouseslip) is a blouse with a petticoat or slip attached to the bottom. Sometimes trim on the bottom of the petticoat or slip is designed to extend below the jumper or skirt.
A petticoat is (at least by simple definition) a half slip with fullness, for wearing under fuller skirts and dresses.

Pettiblouses and Blouseslips
Graceful Threads ~ Made-to-order, with a lot of options.
Katie’s Mercantile ~ A slipdress. Made-to-order.
The Joyful Cottage ~ Made to order in white 100% cotton.
Petticoats
Katie’s Mercantile ~ Two styles of made-to-order petticoats.
Ringger Clothing ~ Ladies 3-tier petticoat with several options. Made-to-order. Also check in-stock items.
The King’s Daughters ~ Made-to-order petticoats.
The Joyful Cottage ~ Made-to-order in cotton muslin.