It sounds like you are just looking at the help database. The header files are on disk, in whatever folder you downloaded the toolkit to. If all you have is the help database, then you need to download the entire kit, from here: http://www.ibm.com/developerworks/lotus/documentation/capi/
It sounds like you are just looking at the help database.
However, it seems you have a misconception or two about what the .h file is. It is C language source code. You cannot include C source code in a LotusScript program! You can use the headers as a reference, find any names and values that you need, and create the equivalent data types and values in LotusScript by hand -- sometimes. I'm not sure what you'll be able to do for DBREPLICAINFO as I haven't got time to take a close look at it right now.
If you want to understand how to use the C API from LotusScript, I very strongly recomend going to this site: http://www.ls2capi.com/