A higher then normal stable temperature unit?

Do you know the refrigerator/freezer brand names with manual defrost. The reason being is, I work in a laboratory and we store enzymes and other biological reagents. These reagents are very delicate and must be stored in a freezer that does not cycle. They need to be stored at about -10 to -20 degrees Celsius without the temperature fluctuating. If you can find out any manufactures that make these units that would be great. Thanks