Me +my Wife visa on arrival against invitation letter ?

I am working in Mexico & shall have to visit to inspect paper machine clothings,ordered in china and like to visit on my return journey from India To Tijuana,Mexcico and also my wife will join me india to come to tijuana via China.
Can we arrive china with my official inviatation letter from The chinese company for the Inspection of machineries beeing imported by us to mexico and also my wife can get visa on arrival beeing accomapnying spouse ,on the way to mexico OR we both shd apply & get Chinese Visa from Delhi & then only shd travel,which may be very dificult due to shortage of time.
Rgrds.Aloke Chatterjee.