Cameroonian consulate in your country of residence.
You will need to submit a visa application form, a recent passport photo, a letter of invitation if you are invited by someone in Cameroon and a bank statement showing that you have the necessary funds for your stay. You will also need to ensure that your travel insurance is valid and covers Cameroon.
Finally, you may be required to attend an interview with a representative of the Cameroonian Consulate. During this interview, you will be asked about your background and your reasons for travelling. Be sure to bring your documents and a smile to the interview.
If you meet the conditions listed above, you should be able to obtain a visa for Cameroon. Make sure you read and understand the conditions of your visa before you start your journey. Enjoy your trip!