Locally, industrial felt is made in three grades and your seal is made from the hardest. One glance at the others and you will understand why.
Unless you have a remarkably well equipped workshop don't think you can cut your own. It needs to be accurate or it will be no better than the one you remove.
In my own case the firm not only provided the material but cut it as well. Not cheap, but accurate. If the firm has a minimum charge for the job see how many you can get for the minimum charge and you then have a few extra to trade or sell.
You don't say which S/A box you are working on but Chaterlea25's suggestion is the way to go if at all possible.
Best of luck.
