Mao can only go to Moscow in early 1950s, since America decided to continue supporting Kuomingtang fleeing to Taiwan hoping to regain mainland China one day. Fairly speaking, Soviet Union helped China a lot, especially in those heavy industry departments in 1950s.

However, Kruchshev wanted China to join that "Warsaw Pact", and he wanted to set up Soviet military bases in Chinese territory. Mao hated the idea of foreign military in China, so that is why Soviet Union broke up with China.

Now, China buys weapons from Russia because China can only buy from Russia. I believe China would be very happy to buy from Lockheed Martin, Raytheon or Northrop Gruman, if they are allowed to sell. China might share similar diplomatic positions with Russia in many international issues, but you are right that the economic ties between China and America is extremely important to China.

I understand why Chairman Mao hated the idea given Chinese history from the end of the Ching Dynasty to 1949. And Russia who has the money to buy the weapons, but I think you are right that China would want to buy from Boeing, Lockheed, Raytheon, and Grumman. However, given the political climate, it is highly unlikely on sensitive materials.