These were offered in Beech Kit form and can be added to your Bonanza. A control cable that is operated from the instrument panel opens an outside air scoop above the rear evaporator box. This evaporator box is filled with water from the outside air-scoop before flight.

Beech Evaporative Cabin Air Conditioner

(Swamp Cooler)
 

www.Filters-now.com  has the plates listed under "Autoflo" manufacturer, P/N 880. I just bought 30 of them for $29.93 including shipping! Grainger apparently no longer carries them.
Click here >  Part # 880 Link 

There are a couple of parts that are either non existent or hard to locate. The first one I will mention is the reservoir shut-off valve, part # 104HD 1/8x1/8. This valve was originally manufactured by a company called "The Imperial Brass Manufacturing Company" Today they are still in business but have gone through many ownership changes and their current product offering does not include the manufacture of the valve anymore. What to do ? Sources for alternative vendors for this two way valve that may in fact be better than the original.

Bonanza A35 owner Chris Nichols sends this information
I have since found and installed a suitable replacement valve mfr'd by Swagelok.  I ended up using valve P/N B-4P4T, 2 ea. connectors P/N B-401-PC, and mounting kit P/N B-5PMK-P4T-BK.  Total cost was about $44 with shipping.  Works great and looks good too! I bought them from Florida Fluid System Technologies, Inc. They are a Swagelok distributor located at 3180 Mulford Rd., Mulberry, FL, 33860. Phone # is 863-425-3222. Mulberry is a bit south of Lakeland, FL. They didn't have the mounting kit in stock so I had them order it and they shipped everything to my house. They were very helpful towards working a solution once I explained what I was trying to do.

PDF sheet of Swagelok Valve