How to find replaement for odd door handle mechanism?

Greetings all!
We have a great glass-paned exterior door we want to keep, but we need to replace the non-functioning handle mechanism that the door currently has. The trouble is, the current handle mechanism seems to be of some obsolete design so we can't find an obvious replacement model.
On the outside, there is a large plate with a thumb lever high on the plate, pretty much parallel to where the latch goes into the doorframe. On the inside, however, the doorhandle is two or three inches below the latch (so there is an additional mechanical bit to allow the handle to control the latch). I presume the nature of this design is why ours failed and why there is a dearth of replacement mechanisms of this type available.
We could adapt the door to accomodate a different system, but this raises some other difficulties (that I won't mention here) so we'd rather find something in the same style with which to repace the existing unit. Does this style of mechanism sound familiar? Is there a name for it that might help me search for a replacement? Any particular online sites I should visit?
Thanks in advance for any advice!
Chuck
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Chuck here again, with a correction to my preceding post: Actually the thumb level on the exterior side of the door is also below where the latch goes into the doorframe; it is a little about the level of the of the interior knob mechanism, but still below the latch.
Thanks!
Chuck
Chuck wrote:

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There are restoration hardware sites on the net, but I don't know of any with actual door mechanism like that, mostly handles, trims, drawer pulls, etc. I don't know if ebay would have something like that either, you could try, browsing through various categories. We have a local Restore Habitat, I believe there are several around the country, and they had a table full of those type of things. Naturally not the kind I need.
If you are patient, I'm sure you will find one. Also you might ask on freecycle. The problem with freecycle is that you can only join your local group(s) usually and the stuff gets snapped up pretty fast. I would not want to wade through the archived posts of all the groups.
Search door latch on ebay. 581 items. There are several listed in Home and Garden and Antiques. H&G includes Building and Hardware, and Antiques includes Architectural and Garden.

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