British Embassy in Santo Domingo????? Forget it!! I think the response from there will be pretty 'non-committal'.
Send an e-mail to the North Coast's Brit. Consul Genni Mendez on
genni_mendez@hotmail.com, tell him what you need (& when you need it by!!!) & ask him how much he will charge for this service & then push him to get the certificate for you once you agree price!
Mendez is a really nice guy, speaks good(ish) English but please type correct punctuation & Capitals when you write to him as his ability to 'interpret' how you write on internet will not match those of natural English speakers!

!! Hope you are not in a tremendous hurry - the task could take 5 or 6 weeks even if he gets a rapid post system back to the UK. As mentioned above, you will have to chase a few times!!
If you want to
really screw things up, you could mention I told you to contact him

- we used to work together & still talk fairly regularly!

!