I'm still trying to figure out why the OP is looking for a 50k FC domestic award when a low level FC award would be 45k miles. No wonder its difficult because there is no such thing as a 50k FC award.

I know it is tough to find a low level F domestic award, it may be beneficial to try and call in and see if an agent can see anything different than the website. Good luck and let us know what the outcome is

Edit to add: As a DM I have actually had success calling in and having the agent see the same thing as me (ie LOW advertised) and then they talk to a supervisor and get them to overbook the low level (45k not 50k, so don't ask the agent for the 50k one or your story becomes less credible) and sell the ticket. No DTC as a DM so might as well call....may play to your advantage where you can name the flights and they just OB them to low level