regex pattern c#

I would like to know if anybody can help me. I want to search a string after this pattern x xxx:xxx in file that looks like this:

content of the file

...
...
customer
1 11:2
material
material data
....
....
EOF

The numbers 1, 11, 2 can be any int number like below:
(int number), [space], (int number), [colon], (int number)

Thanks