new donor lens for old Cord - any suggestions?

Our old Cord (art-deco version) is still very functional, but the taking lens really needs to be replaced. It's a 75/4.5 Triotar. Finding a new front cell is pretty difficult, so if this ain't gonna happen, we'd be looking at replacing the complete taking lens. We'd like to keep the shutter, as it is a good working Compur. It's the kind of Compur where the front cell thread is larger than the back cell thread. Front thread is close or similar to Copal no. 0.

[edit] Oops, wrong turn in memory lane there. The front cell would be something like 22,5mm Ø, the back cell thread 21mm. [/edit]

What lenses would there be that we could use as a good replacement? It doesn't necessarily have to be a 75/4.5, can be 75/3.5 as well. There are plenty of 75mm lenses around on old and tatty folders, but which one is the right fit?

Other option: we will have to replace the complete lens/shutter assembly and find a combination that fits the cord and can be tripped in the same way as the Compur.

NOT an option: replacing the entire camera and getting a better one. This cord is fine except for the lens and we hate to waste a camera that still has some life in it. Moreover, we've got more than enough cameras as it is. We'd end up keeping the cord next to the intended replacement (newer cord, rolleiflex) and would again start asking the same question.

Any tips appreciated.
Norm

The big trick will be that if the taking and viewing lens aren't very closely matched for focal length, you'll have the unhappy choice of making the viewfinder focus accurate at infinity, accurate close up, or at any one chosen distance in between -- but inaccurate everywhere else. That might not matter if you always shoot at f/8 or smaller, but why even talk about an f/3.5 instead of f/4.5 if you don't open up sometimes, right?

One option that does exist if you find a suitable lens (and surely a dead 'cord is a good place to start looking) is to adjust the focal length of the viewing lens by altering the spacing between the front elements, like a front-focusing triplet or Tessar type. This would likely be a "try and try again" operation, but is at least a possibility for improving on whatever focal length match you actually get.

You might look at 6x6 or 6x4.5 folders as a source of suitable lenses; some models of Zeiss 6x6 carried 75 mm lenses, and they were the most common length on 6x4.5 folders. No idea if they'd fit the shutter threads, but many were in Compurs of the same size as yours, so it's at least a reasonable possibility. You might even get an upgrade to a Tessar type lens into the bargain, and if you shop eBay for a camera with junked bellows or body corrosion, you might be able to get a good lens for not much over the shipping.