12" x 10" is not a standard photo size : The US market specific size of 12" x 9.5" is the closest ( 24cm x 30.5cm ) and this is available in virtually all ILFORD Photo Paper products.
The 16" x 12" size ( 30.5cm x 40.6cm ) is a Univerasl product available worldwide again in virtually all our products.
Also I would be pretty sure that other paper manufacturers have these two sizes available in the North American market in the vast majority of their products.
If you ever need to check any of our products, go to the ILFORD Photo website and look up the PAL ( Product Availability List ).
Simon ILFORD photo / HARMAN technology Limited :