delitermar:
I have a two "old targets" which I would be willing to forward. Not sure from your description if either is what you want (the 'original BR-50' target). I will try to describe them below. If either is what you are looking for, let me know.
1st one: It is labeled "Rimfire Benchrest" and off to the side "official target". Four sighters at the top, five down each side, and five at the bottom. There are 25 scoring targets and the bull is about 3/16". There is no indication of the scoring method. The scoring rings are similar to IR 505/50, but have only 6 rings. Full size of paper is 14 1/2" W by 17 1/2 " H. I would describe the paper as close to NRA style, but a bit better.
2nd one: It is labeled "BR-50 International". Copyright is dated 1969. The target was used for Centerfire at 100 yards, Rimfire at 50 yards, and Air Rifle at 25 years. The bull is 3/8". There are fifty scoring targets grouped as 5 per block within 10 blocks. The scoring rings, and scoring method, are virtually identical with the ARA target. Scoring is the outer edge. If you touch the line you get a full score of 100, but if you break the line, your score drops to 50. Full size of target is 14 1/2" W x 11" H. Grade of paper is bit better than NRA targets.
Best wishes finding the target, Doug Miller