Good information to give in order to help better is:
Where is the con being held? A Convention center? A hotel with meeting space? A college campus?
Does your convention use a decorator? Most conventions have a contract with a company to supply the materials needed for a con space. (i.e. tables, table cloths, pipe and hangings, skirts, etc) And so you may have to go through them in order to get your tables.
Often times, hotels are equipped to supply all the tables needed in the meeting rooms. You'll have to talk to your Director of Relations (or whatever the equivalent is for your con) to see what is provided for in the contract for the convention space you are using.
I'm a little curious as to why you are even asking this question. Most conventions don't tell their coordinators "just... get tables. XD"
Also keep in mind that conventions usually lose money on their artist alley, so be prepared to start SMALL (10 tables or less) and build up if you're a baby-con