A lot of istighfar
And you can say as the prophet Moses (( رب اني لما أنزلت إلى من خير فقير ))
You can say as the prophet Zakaria :رب لا تذرني فردا وأنت خير الوراثين  
You can say the duae of اللهم اني بحلالك عن حرامك وأغنني بفضلك عمن سواك 
But there is no specific doua of marriage the important thing is asking Allah and feeling your need to him 
 ask Allah in your soujoud by your own way just ask Allah what you feel with humiliation and fell your poor for Allah's help Allah will help you 
Allah say 
( 186 )   And when My servants ask you, [O Muhammad], concerning Me - indeed I am near. I respond to the invocation of the supplicant when he calls upon Me. So let them respond to Me [by obedience] and believe in Me that they may be [rightly] guided.
Albakarah verse number 186