I work in an office in Oklahoma with less than 50 employees. The company I work for has more than one office in Oklahoma, and several more around the country. Total employees are in the thousands. Does FMLA not apply here just because this specific location has less than 50 employees?

That's correct. The employer may choose to voluntarily provide leave mirroring FMLA if they choose, but if there are not 50 employees within a 75 mile radius, then they not only need not, but cannot, provide FMLA.