You have not found such a site because it doesn't exist --- unfortunately it's not that straightforward.
The only home improvement or repair "grants" that exist (to our knowledge) are offered by the Department of Agriculture. Qualifications include being 62 years old or more and living in specific rural areas. If you meet those qualifications you can find out how to pursue this type of grant either by going to the USDA website or by reading more information in an article called Grants for Home Repair. But be aware that neither of these sites will just present you with an application.
If your home improvement is not considered to be a "luxury item" you might qualify for a HUD Title 1 Home Improvement Loan. These are guaranteed by the FHA so banks are more willing to lend. You need to find an approved lender in your area to pursue this option. You can do an internet search for your town or county or contact HUD's Customer Service line at 800-767-7468.