Try one of the nicer hotels near the conference centre. They usually have a hotel 'business centre' where you can fax for a fee, assuming they haven't stopped with faxes too.
Alternatively, scan and email?
If that's not what you need, try:
wirtualnyfaks.pl
or
tanifax.pl
or
e-fax.pl
Or Google 'popfax' for something similar in English.
We still use faxes at work and I thought they were going to die out. The advantage of fax is that you immediately have a paper document in your hand, however, the disadvantage is that you cannot send it further with one click.