You may be able to just purchase the missing pieces... that particular model should have a securing screw for the arm that may have come loose allowing the arm to pop out. ( see pics in the various links I attach below.
If Gregg at Vintage Motor Cars can’t help, try Cip1. They sell the full assembly, as well as the base ( ref link below. I just ran a quick search). I’m sure with a quick call they may be able to help find the arm (if it’s available and appropriate wiper. Their help desk is super helpful... and they typically carry both German quality to Chinese bargain of the same part.... you choose.
https://www2.cip1.com/ProductD...11%2D955%2D407%2DAPR
If you are near LA, and were thinking of a drive-shopping experience you also have;
- ISP West- they sell the left full assembly only, 25$... and you could just use the parts you need... or ask them if they will sell you just your missing parts.
https://vwispwest.com/wiper-ar...957-left-113955407a/
- WagenWerks - Victorville... longer drive :-). ... they sell new and used... and sell from full assemblies to individual bolts and washers..
https://www.wagen-werks.com/wi...g-1958-to-1964-tops/
https://www.wagen-werks.com/wi...ug-1959-to-1964-swf/
all these places ship as well. give any of these places a call... with your picture they will be able to help... and likely sell you the individual missing parts... that has been my experience with ISP West/Wagenworks. Clip 1 will help find the part#s, and tell you if they have them ( new, they don’t sell used).
hope this helps... cheers,