Plenty to be had. I just searched on the Bay and found several, $22.00 to wayoverpriced. Googling also brought up several possibilities. The standard GG such as the Kodak are rather course grained and your focus won't appear as sharp even though it is sharp. I purchased a SatinSnow 4x5 glass a few years ago and it is excellant, unfortunately I believe he is no longer making GG's but I have seen other brands for sale that look very close. You might check with Jim at Midwest Photo, he may have one. You will need to know exact dimensions minus about 2 mm on 2 sides of the size you need , best to use a millimeter ruler. You want a little wiggle room to allow for expansion/contraction of the wood frame. There are substitutes for GG and I'm sure others will chime in with their suggestions.