coverslip for bonding

Hey everyone,
Thanks for all of the responses for the glass drilling - the response was really amazing.
I was wondering if anyone knew a place where you can purchase glass coverslips for bonding?
For the anodic bonding, it should be type Pyres 7740, however, every coverslip I have seen is borosilicate.
Does anyone have suggestions for getting this type of glass/ in something roughly 25mm*25mm or 25*50mm (size can be different, but on this order)? Or, does anyone have experience bonding with borosilicate or some other glass which can be bought in these rough dimensions? (thickness ~300um)
Thanks for your help,
Max Shulaker