Are we allowed to provide a semen sample through masturbation? I am pretty sure that we are not but would like confirmation from a scholar regarding this issue.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Masturbation is forbidden as explained in Fataawa: 81150 and 83000. So it is not permissible to masturbate even if that is for the purpose of seeking treatment unless it is not feasible to get the sperm through permissible means, like when the person has no wife and he needs this treatment, then in such a case it would be permissible as Allaah says (which means): {While He has explained to you in detail what is forbidden to you, except under compulsion of necessity?}[6:119].

It is only a trustworthy doctor who can determine whether or not you are in a state of necessity, meaning its urgency to prevent harm from afflicting you.  

Allaah knows best.