Why are you making your database server accessible to just ANYONE in the first place? Instead of trying to block selectively, you should permit selectively. In your firewall rules, whitelist your LAN (obviously), any IP ranges owned by the company (for other locations, for instance), and the IP address block used by your home ISP (if, for instance, you sometimes need to do maintenance or emergency troubleshooting from home; if not, then ignore the next paragraph).
If you feel whitelisting your whole ISP seems a little too permissive, then lobby your company to pay for business-class service at your home with a static IP address, OR just take your chances that your DHCP-assigned IP address won't change very often and whitelist your current IP address. (And then check periodically to see if it has changed, and update your whitelist accordingly.) Obviously the solution with the static IP address is safest and most reliable. (If you explain to management the frequency of the attacks, and the risk involved, they might realize that $50/month is much cheaper
This precaution can be used along with other measures, such as:
- using an obscure port
- using fail2ban or syspeace
- a long and complex password
- a delay between login attempts