Keep in mind that plus or minus a few mils (thousandths) is not an issue for woodworking equipment so they are rarely ground perfectly flat over their width and length unless it was a very high end jointer, so it is fairly rare to need tables to be reground unless something major has happened (severe twist, such as from a fire) or there is extreme wear. If the issue is that the tables are not parrallel to one another then that is typically a basic setup issue resolved by shimming the two tables parallel and a part of jointer ownership like setting the knives.
I mention the above solely to ask if you are certain that regrinding is actually required? If it is just a setup issue then members here can squally help you get it resolved and possibly save you the cost of regrinding the tables. Otherwise I wish you the best in your search for a machine shop!