This just came to me... so, of course, there are straight razors where the blade is parallel with the handle. Would it not make sense to have a safety razor like that? Has such a thing ever existed?
I swear I have seen this somewhere - on ebay probably. Straight handles with a DE safety holder, open comb. Looks kind of scary for some reason. Very very old.
Here's something similiar to what you are looking for. Also, I can confirm that the blades for a Durham Duplex are no longer available, although I did speak to someone over on SMF who mentioned the possibility of having a custom spine manufactured for one. The actual company that made these is still in business, so it might be possible.