To my knowledge they are online free in a number of different sites. I believe, whenever he came upon one that was worthy and fitting into the general schema of subjects offered, he too posted them. I understand what you are saying. I do beleive that these authors are long dead and perhaps the copyright too has expired....
In anyevent, I don't really know nor care as good information is like Tzadaka and must be dispursed/given.... imo...