Softmachine72 is doing a really great job of combing the surplus piles of the word for NOS Allen Bradley pots. His 250/500k Mod Pot comes from State Electronics, and apparently they're the only company that has legal rights to reproduce the Allen Bradley Mod Pot of the same architecture. They're expensive...but if you want mil-spec.
I've done extensive searching, as I'm sure many others have. Great pots at Bourns, and PEC as well. The Alpha 250/500 that Waldo has a video on works great. The Alpha pots are available at Mouser if i remember correctly.
Both those pots you're looking for will be available at Stewart McDonald as well, if you prefer to go the $3.00-$5.00 route.
Edit** - You did say quality. I think CTS may have gone back to a higher quality standard than they were a year ago. If you really want the goods...see above.