How to find out who funded a study / research?
Reputable journals might require authors to disclose funding sources, but as noted, this practice, reputable journals notwithstanding, is inconsistent.  Beyond this, there are no standards for determining what is a reputable journal.  

As to the comment that two citations do not prove the point, the literature is replete with studies demonstrating funding bias; a few examples: Pharmaceutical industry sponsorship and research outcome and quality, Lexchen, Bern et al; Avoiding biasing the conduct and reporting…, Hillman, Eisenberg, et al; Systematic review of empirical evidence of study publication bias, Dwan, Altman et al.