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Unfortunately, not. I remember! Dick.biz doesn´t carry it,
but can get it for you as a special order.
The DMT´s they currently have are 120 or 600.
You might get along with each, but the 325 is...

DMT´s come in the following grits:

coarse: Mesh 325
Fine: Mesh 600
extra fine: Mesh 1.200

The DMT coarse, 325 is the recommended grit size for lapping purpose.
You might want to read further...

the 600 grit lapping stone was my first DMT as well.
It works and leaves an outstandingly fine surface.
But as you pointed out takes a little longer.
You should avoid the 1k if possible to prevent...

even though Olivia is a wonderful place to buy it is improtant to know she sells the small versions of the DMT!
Look at the dimensions. You want the ~200x70mm one for lapping etc.

I recommend...