He is refering to an M50 intake manifold... it was produced in the earlier e36s which allowed a higher flow of air than the later OBD 2 cars...
www.understeer.com has them...
You can buy the kit and the manifold together... you have to scroll down one of the option things on the manifold install kit page...
I would just search around... other forums... ect ect.. till you find a used one that someone doesnt want... I wouldnt pay that much money for one unless I was deperate... I paid a lot less for mine...
Good Luck,
Les