Look for bonsai sieves. Linked below is a kit with 1/8'". The largest screen is smaller than 3/8". However they sell the 3/8" (9mm) screen separately.

Zeuspaul

Here is a link that might be useful: Bonsai screens

Great...thanks, Zeus.

Or if you are looking for more generic mesh try McMaster Carr. A one foot square of .12 inch steel mesh is $6.21 and a one foot square of .38 steel mesh is $9.01. You would have to make the sifting frames. I think the bonsai screens are a better deal. However if you want 24 inch square you can get it at McMaster Carr.

With McMaster Carr you don't know the shipping cost in advance. My experience is shipping is VERY fast and very reasonable. I believe it is actual UPS cost and they seem to have a good contract. They are geared toward businesses.

Select *steel wire cloth* in the link below.

Zeuspaul

Here is a link that might be useful: Steel mesh at McMaster Carr

This post was edited by zeuspaul on Tue, Aug 27, 13 at 22:19

I bought 3/8th sieve here: http://www.gardenershub.com/garden-sieve-38-w1370.

For 1/8th, search for "Gold Classifier Screen 1/8" on ebay.