Welcome Stefan!
You're certainly at the right place.
If you don't already have them, books such as Shumways' Rifles of Colonial America-Vol's I & II, works by Joe Kindig, James Whiskers and others, cover many of the different builders, time periods and are must reads.
Often, you'll see someone here pass-on information about auctions that include American longrifles, some by known makers and many others that are not, but are nonetheless, representative of a certain part of the country and a certain time period in our history.
There is even the field of contemporary longrifle collecting and that is certainly to be found here, as well.
Pull up a chair, take a look at the library and use the search feature. What you see here, is only a fraction of the information available to you, on this site.
Good luck!