Some Honda's use the same calipers.
I forget which model honda they came from, but I bought some seals from a Honda dealer. That was a few years ago.
I started by looking for honda's that used the same front brake pads. Not all calipers with the same pads will be the same, some will have different size pistons. It might be hard to check that.
It might have been a 750 Honda Shadow?? Not sure.
Those rubber boots might be easier to match up from another brand. I only chose Honda since that dealer is closest to me, and at the time we did not have a local Triumph dealer.