I use the steel backed plate material, Miraclon MS152, from Gene Becker:
(718) 454 0654
73 - 48 183 Street
Flushing NY 11366
There are other suppliers and manufacturers, with differing depth, hardness,
size, and backing. More details about your plans might get you more specific
suggestions suited to your needs.
I get 10 sheets at a time, size A3 (297x420 mm) for something close to $300
with shipping. The steel backed plates have to be cut with a sheer trimmer,
un-like the polyester backed material which can be cut with scissors; the
depth of the photopolymer material has to be paired with the right backing block
to make it type-high....
Best wishes, Tom
Now It's Up To You Publications
157 S. Logan, Denver CO 80209
[Non-text portions of this message have been removed]