[eg0master]

Nothing is free.
You will need a place to work and most certenly you will need some guidance. I have been helping peaople with master thesis work and leading even the best students takes a lot of time. All this time I put in to help/instruct/manage another person is a cost.
And frankly I do not think 3 months in long enough in order to earn the money that costs me on the work you do.
maybe if you did really simple things (like making coffee, copy papers etc) I would actually make a profit on you but if you are prepared to do that you are either not that good at all (since you are satisfied with real simple tasks) or you are so good that you could get paid to do the same thing. In the latetr case you are stupid not to ask for a salary.

Consider this a warning to you at this forum thinking about using "free work" - nothing is free. And you get what you pay for most of the time.
And to you looking for a short internship - be precise on what you can do expecially without any guidance and ask for a salary (even a small one). You must pretend you are so good you deserve a salary - not beg for a job.