The seal is available from NAPA. Part number NOS 11081.
It's best to use a pitman arm puller to remove the pitman arm.
When it's off, you don't even need to remove the old seal, just clean the surface and install the new one.
This is mine. I just used a banana knife and cleaned the surface up, then installed the new one right on top of the old one - there's plenty of room to do so, plus the old one is a bear to get out.
Here's how it looks when done -
Fill it with lube you're good to go.