Kevin Karst Design Inc. These are available from distributors such as Hafele and Richelieu. Make sure to get the version that has a load capacity of at least 30 pounds. The light-weight ones won't last. The Hafele wardrobe lift product number I like to use is 805.31.223, which is for an installation width of 35 - 47".
Kevin Karst Design Inc. I use what is called a Wardrobe Lift, available through Hafele, a German wholesaler. Check with your local hardware supply outlet for availability. The 33lb capacity version for inside closet widths of 35 1/16" - 47 5/8" is #805.31.223. This is chrome plated with black cases and fittings. The all-black version is #805.31.323.