business visa 12 month multentry with stay 90 days @ time

Dear Sir;

I am an businessman;independant Consultant who wants to apply for 12 month business ;multiple entry with maximum stay 90 days per entry;however normally we only get 30 days maximum per entry.

I have all the documentation;flight tickets;Invitation from Company.Apparantly for more than 30 days;ie 90 days the following additional document is required:

"Invitation Letter of Duly Authorization Unit"to be filled in at the local Municipality Office;which in my case is H/Langzhou in the Gansu Province.

Which exact instructions must I give to my Invitation Company in order to get this letter by tomorrow morning ?