I am trying to find original sources for experiments that had observed spectral lines from hydrogen or other gases. I am looking into experiments that motivated Niels Bohr to write his ideas on the hydrogen atom, but cannot find experiments that may have motivated him.
Bohr's atom became famous for reproducing the Rydberg formula for spectral lines of hydrogen, which Rydberg presented in 1888 and published the next year. Bohr remarked that it was Rydberg's switching from wavelengths to wavenumbers that allowed him to make the discovery. His inspiration came from Balmer's 1885 formula, which was a particular case, and had an integer called "fundamental number of hydrogen" as a parameter. Rydberg's work is briefly described by Martinson and Curtis, who reference the original paper.
In 1908 Ritz generalized Rydberg's formula to a "combination principle", which states that spectral lines of any element include frequencies that are sums or differences of two other lines. He tried to explain it by modeling electrons as vibrating magnets emitting radiation. Here is a link to Ritz's paper.
... papers on Hydrogen spectral lines ... I am looking into experiments that motivated Niels Bohr to write his ideas on the hydrogen atom, but cannot find experiments that may have motivated him.
Bohr was motivated especially by Balmer's formula discovered in the year Bohr was born (1885) and by other more general relations that followed.
The first one who found a formula that gives the distance between some Hydrogen spectral lines was Johann Jakob Balmer in 1885. You can also read the History of spectroscopy for finding who were the first people to see the spectral lines of various elements.