Vintage Suzuki Superbike

Brown is a tolerance code isn't it?

Once new old stock is gone on a part like that, you either make, modify or substitute something that will work, or the machine is on the way to becoming non-serviceable. Seems to me you're looking for 35mm shells with a thickness of exactly 1.5mm and that sounds like something that might have been used on a slew of different machines. If you can't buy it by part number then you will need to buy it on spec. Width, chamfer and holes drilled in them is something you might even be able to work around, an oil passage groove down the middle of the bearing (as shown) would near impossible to add, so if you need that and can't find one with a similar feature, ya'll might be out of the obsolete suzuki racing business before long.

The likely problem is they don't really know what size shells they are making until after they produce it, then quality control has to determine what part they just made and code it, or if they made a piece of out of tolerance range scrap.

How it's made should do a show on them

With a tolerance adjustment range of only 18 micron on the crankshaft journal diameter and 15 micron variation on the bearing shell thickness, I think if Suzuki didn't throw out too many cases and crankshafts during production then they did an admirable job with the machine accuracy. We are talking in measurements smaller then the human eye can see without a microscope.