Thank you for sharing your situation with the Wefugees Community and sorry for the wait!
Indeed, providing a birth certificate is essential in most of the countries for a marriage and not easy to get, if you are not able to travel yourself to your place of birth.
Do you maybe have some relatives or trustworthy friends in your country of origin, who could get a birth certificate for you with a mandate/power of attorney document?
If not, a lawyer in that place might be another possibility.
Can you provide the other required documents as passport, certificate of no-impediment etc.?
Looking forward to hear from you again.
All the best,