heat press question

I just bought a used heat press and didn't really realize until I went to use it that the bottom platen rubber has some indents in it. While I was pressing numbers, if part of a number fell on that indent the backing didn't want to peel off right. I tried putting a sweat shirt over the bottom platen but didn't really help. So can anyone tell me where I can buy new rubber for my press. I check a few places and all I could find was Teflon covers for the platen. The name brand is National so going back to the company isn't really an option.

Help Please
Thanks
BCP
brotherscustomprinting@gmail.com