There are a number of "high-fidelity" Polymerase blends that can amplify long products in a single reaction (I have amplified up to 12kb from gDNA and 8kb from cDNA with Elongase, Life Technologies). However, failing this, it is often easiest to amplify smaller fragments (2-4kb) of the gene (which overlap by about 50-100bp at their termini) with any high-fidelity Polymerase, gel purify the products and mix these together as a template for the final amplification using only the terminal/flanking primers. Hope this helps you.

Yes surely it will help us Mr. Simon. Thank you very much.

Simon J Conn now I am doing with Q5 high fidelity taq polymerase and the PCR product is expected about 12 kb, could you give the PCR reaction and PCR programe that you used to be done, Thanks.