What particular aspect of abortion are you discussing? What links have you given them? And on what facts do they base their assertion that the source is “biased?”
Make them tell you WHY they do not accept the sources-- make them do some work. If the are unwilling to tell you what specifically is biased in the information and how they reached the conclusion the information is biased, then you are dealing with people who are intellectually dishonest and not interested in any actual conversation. You will run around trying to get “acceptable” sources for them, and they will promptly find something wrong with those too.
It is not your responsibility to find ‘unbiased’ sources, it is their responsiblity to refute what you have asserted through doing the work themselves necessary to refute it if they can.