Many useful frequencies from 20kHz on up are standard stock items at digikey. Less than a dollar for a standard value.
Custom ordering one is possible, but will typically be $100+ or so and will have a turnaround time measured in a week or two.
If you just want a square-wave oscillator there are many techniques (including user-programmable or distributor-programmable oscillator modules) that may do the job depending on your phase noise/jitter requirements.
If you want a sine wave oscillator there are numerically programmed direct digital synthesizers for a few bucks that do well for many (but not all) applications.
Tim.