How to get feedback on unfinished research papers if I don't have any direct contact with people qualified in my field?
How can I get feedback on unpublished scientific articles if I have no direct connection with anyone qualified in my field?

Make contact with those qualified in your field.
As an undergraduate, without a reputation, don't expect top-professors to be interested. Aim lower. Personally, I'd suggest a top PhD student or a top postdoc. Someone who's work you have studied and are interested by.
Offer co-authorship.
Don't ask for help, make a mutually beneficial offer: Many researchers are willing to help (this forum is an example), but, everyone is busy, make an attractive offer when contacting researchers. For instance, you could offer your services to help-out on their work, or you could offer co-authorship of your work (in exchange for guidance), or ... Explain your short- and medium-term goals, e.g., publishing your work, developing your profile, getting a post graduate degree, and pursuing a PhD.