in it? TDAmeritrade will not let me purchase a certain stock.

Personally, I don't do ANY investing into individual stocks because its too risky for me.

But, if you've done your research and you want to make that stock purchase, and your broker won't help you, then its time for a new broker. Your broker should work for you, they should give you advice, but let you make your own decisions and SERVE you in executing your transactions. Sounds to me like its time to FIRE your broker.