A 135mm lens on an R-D 1 calls for a finder designed for a 200mm lens on a 35mm camera. Although I think one independent manufacturer (Komura?) did make a 200mm LTM lens, good luck finding the viewfinder as a separate item!
So, your best bet is likely to be a zoom viewfinder such as the Tewe Polyskop, which was available in various ranges. The one I have covers 35mm to 200mm, which in theory means it would cover lenses from about 25mm to 135mm when used on an R-D 1.
However, in practice I've found that there are several nuisances with it:
-- The relationship between the finder and the camera is such that when you look through the finder with your right eye, the tip of your nose wants to go right smack into the camera's viewfinder eyepiece, leaving a big greasy smudge! Don't laugh... having to stop and clean off the eyepiece frequently is quite a bother.
-- Framing is so critical that a slight mis-setting of the finder's focal length control or parallax adjuster can lead to drastic framing errors.
-- Another source of framing errors is that it's hard to line up the finder in the accessory shoe so that it points exactly the same way as the lens.
Because of all these problems, when I use a 135mm lens on my R-D 1 (which I only do rarely because of the inconvenience) I tend not to use an accessory viewfinder at all! Instead, once I've got my basic shooting situation lined up, I shoot a test shot, check it in the LCD to see what's included in the frame, then take subsequent pictures by using the rangefinder patch as an aiming reference and relying on memory to know what else will be in the picture.
If you want to see what a Tewe finder looks like on an R-D 1, and see some rough framing-accuracy tests with several lenses, my old page on this subject is still up at
homepage.mac.com/jlw/photo/R-D1_finder/