hey allan

see if you can find a 21 cm 3.5 tessar.
it is a great lens ...

that said, its around 1/2 a stop more light ... not really sure if in the end it is worth the big bucks for 1/2 a stop ...

there are some less expensive alternatives though ...
you might see if reinhold here on apug has something around that FL ... he builds fast old school wollaston lenses
or harvest something out of an old folder and make your own fstop/choke ...

have fun !
john