[link=http://www.jjorly.com/g10_fr4_sheets_fabricator.htm]http://www.jjorly.com/g10_fr4_sheets_fabricator.htm[/link] has a competitive price, they just sell in 3ft x 4ft sheets...
Plus I called the company (JJ Orly) today and they said that they also custom cut parts and special sizes out of G10 for the RC community.

When I looked on Mcmaster Carr, I couldn't find a 4" x 6" piece anywhere...and I use Mcmaster all the time. The only size they had that was close to 4 x 6 was 6 x 6 x .625 and it was $31.25, almost 3 times the cost per square foot of the 3' x 4' sheets mentioned above. I also buy G10 board quite frequently would question the true integrity of the material at $9.00 per 4x6" block.

What catalog page on Mcmaster was it on?