Hello, hope you are having a good day.
Unfortunately the BIOS chip itself was never sold seperately. It would require a system board repalcement. I have had customers in the past purchase them and install them with much success. Due to the age of that particular workstation I am not sure HP still has parts available, however HP Parts Driect could certainly tell you for sure. They can be reached at 1-800-227-8164.
Best Regards,
Wendy_R