In the Personal Info section of TurboTax, enter your state of residence as FL, and indicate that you had "other state income" from MO. This will prompt the program to produce a non-resident MO tax return.
Complete your federal return first, including your capital gain. It should then flow to Line G of your MO-NRI. The TurboTax program will calculate your MO tax.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.