I have found a Honda pin that will fit the bill (~70mm). This pin has a hex head which will take an 8mm hex socket, much more robust than the 5mm internal hex. Honda Part No. 43215-KZ4-J41 is in the top part of the photo, with the OEM Yamaha pin below for comparison. Note extra thread length, etc. but the important part is the length to capture the brake pad. You don't have to have the O-ring if you lose one, it only serves as a guide as you insert the pin. See also the photo of both installed in an FJR front caliper.
The Honda pin costs ~$3.40, application is rear brake caliper of '08 CBR1000 and CRF450, perhaps other models. If you prefer a 5mm hex, perhaps try 45215-MAJ-G41, also 70 mm, but I have not verified this with a part in my hand.

