Todd Howerton, owner of a company called Outlaw Disc Brakes, who is well known in E24 circles, and Alpina circles as well, is well versed in rebuilding these guys. I just texted him about these bolts as he usually has good suppliers for hard to find parts. His answer to me is they are near impossible to find and he has redrilled and tapped the calipers to the next size up in the past with great success and at that point could use readily available fasteners. Todd is pretty anal about both his work and his cars and I would take what he says as something to give some thought to. You might also check his website as he manufactures some very nice products