那时我们公司正在寻找中国发电机供应商。

it sounds a little unnatural, but the problem is not with the placement of the word "中国".

那时我们公司*在中国*寻找发电机供应商 means "At that time our company was looking for a generator supplier *in China*". This statement sounds like you want to slightly emphasize that you were in China at the time.
那时我们公司正在寻找*中国*发电机供应商 means "At that time our company was looking for a generator supplier from China." This sentence does not tell the reader where you are at that moment, it tells the reader that you are looking for a person or organization.

because you used 那时(at the time), readers will think you are stating an "action that has been going on for a while" or a phenomenon/state that has been going on for a long time , so it's better to say 正在寻找(be looking for) or 想要寻找(intend to look for).
e.g. 那时我们都很年轻。(We were all young at that time.)
那时我正在参加考试。（I was taking an exam at that time.）
那时我想和妈妈一起去北京。（At that time I wanted to go to Beijing with my mother.）←the desire to do something for a certain period of time

我被派去中国出差，要参观几些家供应商的工厂、进行谈判、收集主要信息。

1. people say 几家 or 一些 to mean "some/several", but they don't mix them.
几家 is more formal than 一些. 一些 is more common in spoken language.

2. I thing 谈判 is ok in this context.
商务谈判=business negotiation
people usually omit it as 谈判.

我还访问了力帆公司，一家有名的汽车厂商，他们也制造汽油发动机和发电机。

Sinophone world has absorbed this sentence structure from English, for example, "乔布斯先生，一个新来的程序员，对我们公司很重要。"（Mr. Jobs, a new programmer, is very important to our company.）
↑ a noun or pronoun can be followed by a noun (or other form that plays a similar role) that explains or adds to the former, which is, to put it bluntly, an extension of the content of the preceding noun.

This is grammatically correct.
But if this explanatory part is a bit long, especially a noun with an adjective modifier (like 一个新来的程序员/一家有名的汽车厂商), it's a little unnatural. It makes you sound like a character who stepped out of a dubbed film.
It would sound more natural if it were worded as follows:
我还访问了力帆公司。这是一家有名的汽车厂商，他们也制造汽油发动机和发电机。 (I also visited Lifan. This is a famous car manufacturer, and they also make gasoline engines and generators. )
In other words, it's good to break it down into two sentences.

Well, not a big deal. Native speakers sometimes write sentences like this, too. just old-school intellectuals (like my headmaster) don't like this usage and wanted to correct the trend. XD

那时我们公司在中国寻找中国发电机供应商。

我被派去中国出差，要参观几些家供应商的工厂、进行谈判、话、收集主要信息资料。

谈判 有点太过嚴重了

我还访问力帆公司，他是一家有名的汽车厂商，他们也制造汽油发动机和发电机。

通常我我一般用英语跟中国供应商交流，但是力帆经理有一个俄文翻译。

尽管那个翻译有中国人的外貌／長得像中国人，但是他的俄语说得非常流利，都没有口音，所以我认为他是来自俄罗斯的人。

谈判会议结束后我们都去吃晚饭。

这就是因为他目标明确和积极主动!