The Autoflo 707 model has been discontinued for years so the evaporator wheel and disks are no longer available. If you need those items you need to replace your humidifier. Below you will find a link to buy a unit labeled a Skuttle model 86UD. That unit is made by another company but is similar in design, installation and function to the Autoflo 707.
4001 Saddle Valve
4001On Sale $15.50
50333 Multi Tap 24 Volt Transformer
50333On Sale $29.48
Skuttle 86UD Under Duct Drum Style Humidifier
86UDOn Sale $302.28